The Des Plaines Park District has closed its Lake Opeka to boating, fishing and other recreational activities after workers discovered potentially toxic blue-green algae in the water Tuesday.

The closing means all Lake Park Marina operations, including paddle boat and kayak rentals, the Sailing Club and fishing boat launches are postponed indefinitely. No fishing bait will be sold sale in the clubhouse during the closure, and the Izaak Walton Fishing Derby scheduled for Saturday during the district's Fall Fest has been canceled.

The park district also is urging people to stay out of the water and to keep their pets from entering or drinking from the 40-acre lake at 1015 Howard Ave.

Park district Executive Director Don Miletic said the lake algae was being tested Wednesday and the Illinois Environmental Protection Agency determined levels were within the range that caution is necessary.

"The standard course of action is to ride it out," Miletic said Wednesday. "Let it do it's thing and it will go away. That can take anywhere from five to eight days up to two weeks."

The park district will remove warning signs that are posted around the lake and post updates on its website and social media pages when it's safe to resume recreation activities on the water, he added.

Similar blue-green algae blooms have popped up across the area and around the country in recent weeks, in some instances leading to reports of dogs falling ill or dying after drinking or swimming in tainted water.

Any person or animal who comes in contact with a possible algae bloom should immediately be rinsed off with clean, fresh water, experts say. Symptoms of exposure to toxic algae include rashes, hives, diarrhea, vomiting, coughing or wheezing.

Algae blooms are microscopic organisms that occur naturally in lakes, streams, rivers and ponds, according to the IEPA and the Department of Public Health. Most are not toxic.