WESTPORT — Swimming is prohibited Monday at the town’s Long Island Sound beaches in the aftermath of heavy rainfall Sunday.

The beaches are open, as temperatures approach 90 degrees Monday afternoon, but the water is off limits, according to a statement posted by the Parks and Recreation Department.

Parks and Rec officials, acting at the directive of the Aspetuck Health District, routinely prohibit swimming when rainfall has reached an inch or more within a 24-hour period — as was the case Sunday.

State officials, however, report Sherwood Island State Park in Westport remains open for swimming.

A report posted by the National Weather Service says Westport received more than an inch and a half of rain Sunday, while other Fairfield County communities — particularly in the Danbury region — were socked with three to four inches.

Heavy rain has the potential to wash contaminated runoff and overflows from sanitary sewage systems into the Sound, posing health risks to swimmers.

An additional risk factor, officials said, is the “unprecedented” rain that triggered record flooding in parts of Vermont and New Hampshire, which is swelling the southerly flow of the Connecticut River with “debris and pollutants” emptying into Long Island Sound.

For updates on the status of swimming at local beaches call the Parks and Recreation Department cancellation line at 203-341-5074.