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Love for lake turns it from a mash of algae into a recreational oasis

Can you fall in love with a lake? Eeva Ståhle from Naantali went to look for the lost spring in Viluluoto but ended up finding a lake. Soon she founded the registered association ProLuolalanjärvi to save the lake.
Six people on a dirt road in the countryside.
Planning to protect a wetland. © Eeva Ståhle

Lake Luolalanjärvi is located right near the centre of Naantali and has a beautiful shape. For the last 60 years, the lake has been badly treated. It is severely eutrophic, which can be seen in the cyanobacterial blooms every summer.

“I got clues about the spring and spent an afternoon running around the bushes along the drainage ditch, but I couldn't find the spring. Then I crossed Armonlaakso road, and then, at the tip of the Viluluoto headland, I could smell a fresh scent despite the blue-green algae covering the lake,” says Eeva Ståhle.

From that moment began an exciting exploration into the history of Viluluoto, Naantali's first health spa, and Lake Luolalanjärvi.

“Amidst all the hustle and bustle, I fell in love with Luolalanjärvi. It has been the most important place in Naantali after the monastic period was over and only a few hundred people lived in Naantali. Numerous nobles and high-ranking officials from Sweden, Russia, and Germany have come to the lake to take care of their health – along with other guests at the spa.”

Past negligence can be corrected

A woman holding a Secchi disc.
The transparency of water is measured with a Secchi disc.© Eeva Ståhle

“The hardest part was that at first no one really believed in what I saw and knew was possible. I was sure that the lake could become a real oasis of recreation, even if it meant many years or work.”

2020 was the first year of ProLuolalanjärvi association’s operations. A few families attended the founding meeting. Everyone was excited about the idea that the condition of lake could improve.

“We didn’t have any funding; it was all started with a collection carried out with the permission of the police. It was wonderful to see the people of Naantali join in without question. We were modest, we asked people for at least one euro. Many donated 10–50 euros. We had to stop the collection after a couple of weeks, because we had already received enough money for the procedure we intended and could not collect for other purposes.”

A number of private companies also pitched in. With the initial capital, the association got the city to participate in the research. The association wanted to know many things about the lake, such as what fish live in the lake and how many there are, what the mercury content of the fish is as well as the concentrations of other heavy metals, what the state of the benthal deposit is and how much external load the lake receives.

Due to media coverage and the enthusiasm for outdoor recreation during the pandemic, people began coming to the lake. Visitors have come especially from Turku and Raisio, even by bus. This has also shown in the visitor counter, which was installed by the nature trail. As the number of visitors increased, cooperation with the City of Naantali intensified.

“The first thing we did was to clear up some trees and bushes on the Viluluoto headland. The city cut down the trees, we promised to clean up after. The city workers couldn't believe their eyes when we cleaned the area in just a couple of sessions. That's how we built trust. It has been great to get to know and collaborate with people who work for different sectors of the city.”

Results on the condition of the lake are encouraging

Two people holding a sampler on lake ice.
Measurements on lake ice.© Eeva Ståhle

Last year, the most visible result of the remediation project was the completion of in-depth research results related to the state of the lake. The results are a strong help in justifying further action. The ELY Centre in Southwest Finland came to help by offering to make graphs of the research results that are easy to understand even for the uninitiated.

In addition, ELY carried out an acoustic survey of the lake, with the help of which a depth map was made and the water volume could be more accurately calculated. ELY subsequently offered to commission a wetland plan to be implemented with funding from the city and the Ministry of the Environment.

“Last autumn, we did experimental fishing with nets with the Southwest Finland Fisheries Centre. We emptied the nets and saw how the counted and weighed fish turn into a prediction of the lake's fish stock. It is estimated that around 90 per cent of the fish in the lake belong to the carp family.”

This summer, the lake has been fished for tench with ten traps rented from the Fisheries Centre. In a few weeks, we have caught almost 100 kilos of fish. Although trap fishing alone does not help to balance the lake's over-dense stock of cyprinids, fishing has provided important information on, for example, the lake's strong population of pike, perch, and crucian carp.

“Recently, we commissioned an oblique sounding at Luolalanjärvi to find out if it is possible to fish with a seine net there. An appropriate area has now been marked and we hope that our funding application will be successful and that we will be able to seine in the coming autumn. Successful removal of fish always has an impact on the state of the lake.”

ProLuolalanjärvi received funding from the ELY Centre for the preparation of a remediation plan. That is now the next step.

Remediation of a eutrophic lake is an arduous task

In the summer of 2022, the lake has appeared completely different from the previous couple of summers, when it has been under observation. There was no blue-green algae or even green algae until the beginning of August, and the visibility depth has been about 140 cm, with the water being very clear. In the previous summer, the visibility depth was at its worst only about 15 cm.

The lake is surrounded by a two-kilometre-long nature trail. It is charming and varied and allows its visitors to experience the lake up close. Sometimes the path climbs up to where the lake can be seen from a height of several dozen metres.

In summer, the lake’s shores are lined with abundant aquatic vegetation: filamentous algae and massively amounts of hornwort. There was no exception this summer. “The beaches look really disgusting, and swimming doesn't come to mind even on the hottest days,” says Eeva. The lake is overly eutrophic and requires real action in order to even get its classification down to eutrophic.

“The lake is currently a good research and study object and provides great opportunities for exercise. You don't have to go to the gym if you row across the lake to check the fish traps, cut the vegetation along the nature trail with a scythe, or cart gravel or wood chips to the trail. My greatest hope is that people will be able to find what I have found, each in their own way, and that they will volunteer and help us with their own hands,” Eeva encourages. 


Finnish Environment Institute (Syke)