Warning signs have been put up advising visitors to Burnham's Apex Leisure Park to avoid its lake due to the presence of toxic blue-green algae.
Sedgemoor District Council asks both people and their pets to avoid any contact with the water and to follow all signs and guidance on the site.
Apex Leisure Park remains open while samples of water are to be tested by the Environment Agency.
A council spokesperson said: "Despite the presence of blue green algae in the waters of Apex Park Lake, there is still plenty to do and see in the 42-acre park.
"Visitors can go skateboarding; use the outdoor gym, play facilities, as well as just enjoying a walk and the wildlife."
The algae, known as Cyanobacteria, usually bloom in the summer with no quick or easy remedies to control the blue-green algae once they appear in a lake or pond.
These produce toxins can kill wild animals, livestock and pets. They can also harm people, causing rashes after skin contact and illnesses if swallowed.
Fishing is permitted, but the rules relating to blue-green algae provided on permits must be adhered to.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here