Dredging in Hollola frog habitat was 18 times larger than reported

Extensive dredging on Lake Vesijärvi in Hollola was up to 18 times larger than reported to authorities and likely caused significant environmental harm, according to Yle.

The work was carried out in the Laitialanselkä section of the lake between 2023 and 2025, between areas belonging to a Natura nature protection area. Hollola’s environmental protection authority said the information in Manskivi’s permit application was partly incomplete and possibly inaccurate.

The first dredging operation was reported as covering less than 1,000 square metres. The Häme Centre for Economic Development, Transport and the Environment estimated that aquatic vegetation was removed from about 1.5 hectares, making the area roughly 18 times larger than reported. A second operation was also considerably larger than declared, covering an estimated 1.5 hectares instead of the reported 1,000 square metres.

Authorities are concerned about the impact on protected species. The area has previously been known to host the European tree frog and two species of dragonfly, the white-faced darter and the dark whiteface. No nature surveys were carried out at the dredging sites before the work began.

According to the authority, the dredging may have destroyed breeding and resting places for protected species. It also removed aquatic vegetation across extensive areas. The vegetation helps bind sediment along the shore and provides habitat for organisms.

The environmental protection authority said the dredging probably weakened water quality and the ecological condition of the water system. Long-lasting water turbidity caused by the work can also be seen in aerial photographs, it said.

Some of the dredged material was deposited at a former gravel extraction site in a groundwater area near the Laitiala water intake facility. The authority said the material may have harmed groundwater quality and wants a sample taken from a groundwater monitoring well.

Dredged material was also used to fill and pipe a stream over a distance of more than 200 metres. According to the authority, this may have caused nutrients to run back into Lake Vesijärvi. The permitting authority is investigating whether piping the stream required a permit under the Water Act.

Hollola’s environmental protection authority said granting a permit retroactively would be difficult because the environmental damage has already occurred. The permit process should nevertheless consider measures such as restoring vegetation along the shore.

The company that carried out the dredging said its aim was landscape management and landscaping. The Permit and Supervisory Authority is currently processing Manskivi’s permit application, and Hollola is expected to submit its statement on the matter in September.