The Barker’s Island swimming beach was closed Friday, Sept. 10, after city officials observed algae blooms at the beach.

It’s not clear how long the algae will remain an issue.

In Wisconsin, blue-green algae blooms generally occur between mid-June and late September, although in rare instances, blooms have been observed in winter, even under the ice, according to the Wisconsin Department of Natural Resources.

Blue-green algae blooms can produce toxins that make people and animals sick after they swallow, breathe in or have contact with affected water. The algae is a photosynthetic bacteria that many people refer to as pond scum. It is most often blue-green, but can also appear blue, green, reddish purple or brown.

In humans, exposure can cause symptoms like stomach cramps, diarrhea, headache, fever, muscle weakness and difficulty breathing. People should contact their doctor or Wisconsin Poison Control at 800-222-1222.

Newsletter signup for email alerts

In pets it can cause seizures, vomiting or diarrhea; contact your veterinarian right away.

City officials are cautioning people not to swim or walk along the banks of water with algae, and to avoid swallowing affected water.

The beach is closed for swimming and conditions are no longer being monitored for the season.