Zagreb Speleological Union: Clean Underground

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Zagreb Speleological Union: Clean Underground

Project Status: 2015-2025
Location: Croatia

Croatian mountains are located in the centre of the karstified Dinaric region. A key geomorphologic feature of the area is the formation of speleological objects: 10,000 caves and pits have been discovered. These passages connect surface waters to groundwater aquifers, so their preservation is particularly important for freshwater supply. As home to hundreds of unique species, our underground is also a globally recognized biodiversity hotspot.

It is widely recognized that caves are fragile habitats, with little capacity to absorb pollution. Through the Clean Underground project, we have documented over six hundred illegal waste dumps in speleological objects. Recognizing this epidemic, we set a strategic goal to improve the health of our mountains and their underground in order to prevent habitat degradation and groundwater pollution.

We organize clean-up campaigns with the local residents and environment protection authorities, educate from elementary schools to colleges, and cooperate with government authorities on relevant legislative issues. We have significantly impacted the visibility of this problem in the media, local communities and government institutions alike, establishing our project as a starting point in cave protection issues. We have applied for EU grants in order to professionalize and widen our efforts locally, and in the Dinaric region.


Karst underground and its rich fauna are among Croatia’s fundamental values whose protection has lasting impact on our mountain areas. Cave protection is a complex problem: the underground is largely unexplored, difficult to access, and its significance is not appreciated in the educational system or the media. Relevant legislation is incomplete and contradictory, further complicating cave preservation. Therefore, our long term goals to protect karst mountains, prevent habitat degradation and groundwater pollution require diverse and well-planned efforts.

On illegal underground waste dumps, communal and building waste is the most common, followed by large waste (cars, washing machines, stoves). A specific problem in cave dumps is animal remains (slaughterhouse/butcher waste, livestock, game animals and pets) that pose a threat from microbiological contamination of groundwater. Explosive devices ranging from World War One to modern times are an imminent threat to speleologists and public safety, and a source of heavy metals contamination. Since 2015, in collaboration with different state and NGO’s, we have cleaned 32 cubic meters of waste in ten clean-up campaigns across our mountains. We have assisted the Anti Explosive Troops of the Ministry of the Interior in removing 41 explosive devices from caves. All our campaigns are advertised in local and national media, shedding a light on these issues for the first time.

We built as a starting point for cave protection issues, especially the problem of underground waste dumping. Speleologists are advocates of karst exploring and protection: we educate the caving community by regularly lecturing on courses and congresses. Keeping our drinking water safe and preserving biodiversity are issues of universal importance so we also lecture across primary schools, middle schools, universities, libraries and mountaineering associations. We have given over twenty talks (some available online) to the widest of audiences.

Long term preservation of the underground in karst mountains must stem from legislative protection. Through extensive collaboration with the Ministry of Environment and Energy, we have encouraged significant change in the legislation concerning cave protection. As a result of our work, the problem of polluted underground was included for the first time in the Waste management plan of the Republic of Croatia. The locations of polluted caves were recently also published on state digital databases, administered by the Croatian Agency for the Environment and Nature (Bioportal, EnviPortal). As recognition for our work we were awarded the National Prize for the Best Environmental Protection NGO project in 2016.

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Karst aquifers are Croatia’s main water source and implementation of the Clean Underground project improves the quality of drinking water. Carried by water, karst pollution can permeate quickly without filtration and spread to remote areas. Entire villages and towns still use caves as waste dumps, unaware that they are polluting their springs and water wells. Local communities are not familiar with these concepts so education is essential in order to prevent future incidents. Cave clean-up campaigns are an ideal opportunity to include the (local) media and residents and attract public focus to the problem.

The first cleanup campaign was organized in 2015 in the Mountain District. We collaborated with the City of Slunj, Volunteer Fire Department, Red Cross, Mountaineering and Hunting Club in cleaning over five cubic meters of communal and animal waste from a complex vertical pit, restoring its natural state. A World War II explosive device was extracted in collaboration with the Anti Explosive Troops. Local utility company disposed of the extracted waste, and distributed flyers to all households in the area informing the locals about the Clean Underground project and the clean-up campaign. The event was extensively covered by local radio stations, national and commercial media.

On Earth Day 2017 we organized an event with the Nature Park “Učka” and the local utility company at the top of Mt. Učka (Rijeka). A similar event will be held annually, given the number of polluted caves in the area. Around 100 local residents, including school children from the nearby towns and villages visited the event and participated in the lectures, workshops and cave-cleanup demonstrations. Two pits were cleaned in the primary public water supply protection zone and were therefore top priority in keeping the water supply safe. The event was covered by national media.

The city of Ogulin is famous for its Đula-Medvedica cave (16,396m) whose underground channels stretch under the city. The unique position of the cave is also its curse, since both of entrances are littered with huge amounts of communal waste that is carried deep into the cave by the river Dobra. To warn of these issues, we have organized a cleaning campaign and a public presentation of the Project. Similar event including clean-up campaigns and education was organized in the Mt. Žumberak area (Samobor) where we cleaned the Medjame cave in collaboration with the local nature protection authorities and local media.


All cave clean-up campaigns are organized in collaboration with local authorities, but to solve a national problem we have to think broadly.

According to existing Croatian legislation, speleological objects are protected and monitored by the National/Nature Parks and the appropriate county Public Institutions for the Management of Protected Areas. However individual counties, districts and cities are responsible for the recovery of waste from illegal waste dumps on their surface. Underground waste dumps are not defined by law, i.e. they are in a legal grey area which results in a deadlock in all formal action regarding cave cleanup. Due to the complexity of the problem, it is our strong belief that adequate mountain and cave protection cannot be achieved through individual action without legislative involvement by the government institutions. For these reasons, one of our goals is to collaborate with the Ministry of Environment and Energy (Ministry) in order to fill these legal gaps.

Through intensive meetings with the Ministry we have, for the first time, succeeded in incorporating our data in the Waste management plan of the Republic of Croatia for 2017 to 2022. As a fundamental national waste management document, by law this plan must be consulted upon drafting of regional, operative waste management plans. Stemming from this fact, illegal waste dumps in the karst mountains of Croatia cannot be ignored anymore as an ecological and waste management problem.

A separate problem in proper cave management is the reporting illegal waste dump locations. By law employees of the local utility companies should report and also organize the cleanup of the material, neither of which is possible. When waste is dumped in isolated mountain areas, especially in sinkholes and pits this law cannot, and is not enforced. In order to solve this issue we have collaborated with the Croatian Agency for the Environment and Nature, a central state data collection point for nature/environment based issues. We have succeeded in publishing our data about polluted Croatian caves and pits on the Bioportal and the Environment Portal – two relevant GIS-based databases administered by the Agency. What’s more, the data for each polluted location is linked to the Clean Underground website, providing additional data (photo galleries, detailed descriptions). This governmental acknowledgement of our data enables officials to find relevant information regarding karst underground pollution through official digital databases, helping them plan future policies in order to start solving this issue top down.

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Waste management is recognized as a primary problem in nature protection in Croatia, and illegal waste dumping is a national epidemic. Unfortunately, “business as usual” regarding its clean-up almost means no business at all! The environment protection sector was introduced to the problem of waste in karst caves and pits through the Clean Underground project. We have established ourselves as relevant experts and partners to the Ministry of Environment and Energy in shaping the legislative regarding the protection of speleological objects. Indeed, the Clean Underground database, as published on the state Environmental Portal is the first published data set regarding illegal waste dumping in Croatia.

Due to complexity and dangers of organizing waste cleanup from karst pits, members of the caving community are needed to do the work. We have gathered a team of experts that can cope with the most difficult and dangerous types of waste found in the underground. Alongside cavers, on our campaigns members of the Croatian Mountain Rescue Service are present to assist with the highly technical details of rigging needed to safely extract the waste, and intervene in the event of possible injuries. Professional firemen have helped us extract large waste, for example by cutting and extracting a car wreck in a 35 meters deep pit in nature Park Žumberak – a feat that was never been achieved in the region. Cooperating with the Anti Explosive Troops of the Ministry of the Interior we have removed in a single mission 31 explosive devices (weighing over 100 kg combined) from a deep and narrow karst shaft – also a feat that has never been performed in the region, and possibly worldwide.

In addition to cleanup campaigns, we have catalyzed public education, media promotion and most importantly cooperation with the legislators to establish proper and long term cave preservation. One of the key hurdles to karst underground protection is the difficulty of inspection by nature protection authorities. We are currently developing an innovative monitoring system using customized drones capable of descending into karst pits to assess their state. Implementing such a system will empower nature protection officials to monitor karst underground in a cost efficient, safe and sustainable way. This leap forward will bring significant benefits to the protection of karst caves and mountain regions in general.

Clean Underground is thus a worldwide unique volunteer initiative that gathers caving enthusiasts determined to preserve what they love.


Zagreb speleological union (ZSU) gathers 350 cavers in the Zagreb area. A significant part of our activities is karst protection through cooperation with state institutions, local authorities, universities, companies and NGO’s. We have launched the Clean Underground as a volunteer-based project with Ruđer Novak, Ph.D. as its leader, and cavers across Croatia contributing equally. The project is financed through cleanup and educational projects. ZSU received a national prize and the support of over 20 public institutions for our efforts.

Given the complexity and scale of the issue at hand, it is clear that long term engagement is necessary to solve the problem of karst underground pollution. Several important milestones have been reached: the unification of data from 22 caving organizations was a key step. The following milestone was the publication of a worldwide unique polluted caves database with 679 entries, backed by 299 photo galleries. Using this data we annually organize three clean-up campaigns, dozens of lectures and media appearances, making the Clean Underground the first line of defense for underground habitats. Realizing the complexity of the problem, the third milestone was integration of our data into the national legislation in cooperation with the nature protection institutions.

Our short-term plan is to organize volunteer clean-up/education campaigns and continue to put pressure on the government institutions to propose changes that will prevent the pollution of our mountains. As mentioned, we will also empower the relevant authorities with a simple and innovative system that will enable efficient cave monitoring. Currently we are upgrading, redesigning and translating the Project web page in order to communicate our cause more clearly.

Our mid-term plans include applying for EU financing and broadening the project to the regional (Dinaric) level. Illegal cave garbage dumps are no local problem: the whole region faces these issues, especially in the densely populated areas. Groundwaters of the Dinaric karst hold high quality water in some of the world’s largest karst aquifer systems, so keeping the underground clean is of universal importance.

On the longer time-scale we plan to put an end to karst pollution through educational campaigns. Through extensive cooperation with the local and national authorities we will lead and coordinate cleaning of the Croatian underground, county by county. The gained knowledge will be transfered regionally through colaboration with the caving communities in the Dinaric area.


Responsible use of groundwater and protection of unique cave fauna are national strategic goals. Clean underground promotes protection of karst mountain areas through engagement of volunteers in local communities. Our project has made significant impact and echoes all over Croatia, especially in the environment protection sector. In 2016 we were awarded a State Prize by the Ministry of Environment and Energy for the best Croatian NGO nature protection project.

In 2015, on the World Environmental Health Day (September 26th) the famous freeclimbing centre National Park Paklenica organized a volunteer cleanup campaign of a secluded pit uder it’s jurisdiction. The park’s employees learned about the pollution through the Clean underground web site. The independently organized event included local residents, local caving clubs and Park employees: garbage was extracted from the pit and carried in bacpacks down the hill. As stated by the National Park, the event was organized in support of the Clean underground project.

Inspired by our Project, Nature Park Učka, organized on Earth day 2017 the first annual cleanup campaign in one of its many polluted speleological objects. Through our web they too have learned about the 20 caves and pits filled with garbage in the area they protect, and have decided to cooperate with the Project in an attempt to clear their underground of waste. It is planned that an annual event will be organized, that will include a clean-up campaign, lectures and workshops for the local schoolchildren.

The awareness of the need for stewardship in the mountains, but also in their underground in order to protect karst and use it sustainably is quite low. This is true in the government sector, but especially in the communities that are not aware of the importance of caves. That is why we invest significant efforts to educate: we annually hold lectures about the dangers of karst pollution to students of nature protection related Faculties on the University of Zagreb. To these issues we have introduced future generations of engineers of the Faculty of Science – Departments of Biology and Geography, Faculty of Forestry and Faculty of Mining, Geology and Petroleum Engineering. We also regularly hold lectures at different caving and mountaineering clubs in order to sensitize the people that spend time in the remotest of mountain areas. Owing to this targeted education, we have succeded in engaging the public and thus receive new information about polluted caves on a weekly basis.


Zagreb Speleological Union/Clean Underground