The weather forecast is perfect for a day at the beach this July 4th. But more than 20 lakes and ponds are closed for swimming across Massachusetts on Friday.

The closures are mostly due to high levels of bacteria in the water. In Concord, the main beach at Walden Pond is closed all summer because construction of a new bathhouse poses safety concerns to the public. 

The Massachusetts Department of Public Health has an of water quality test results at local beaches. Below is the list of beaches that were closed for swimming as of 8 a.m. Friday, and the reason for the closure.

Damon Pond Beach, Ashby (Other)
Brackenbury, Beverly (Bacterial Exceedance)
Flax Pond, Brewster (Bacterial Exceedance)
Upper Mill Pond, Brewster (Harmful Cyanobacteria Bloom)
South Pond, Brookfield (Bacterial Exceedance)
Walden Pond, Concord (Other)
Sandy Beach, Danvers (Bacterial Exceedance)
Moses Smith Creek, Dartmouth (Bacterial Exceedance)
S. Sunken Meadow, Eastham (Bacterial Exceedance)
Upper Highland Lake, Goshen (Bacterial Exceedance)
Magnolia @ East, Manchester (Bacterial Exceedance)
Lulu Pond Beach, Pittsfield (Other)
Children's Island - Back, Salem (Bacterial Exceedance)
Willow Avenue, Salem (Bacterial Exceedance)
Peckham Pond, Saugus (Bacterial Exceedance)
Sunset Beach, Shrewsbury (Bacterial Exceedance)
Lake Wyola, Shutesbury (Bacterial Exceedance)
Beamans Pond - Campground, Templeton (Bacterial Exceedance)
Beamans Pond - Day Use, Templeton (Bacterial Exceedance)
Seth's Pond @ Town Beach, West Tisbury (Bacterial Exceedance)
Lake Dennison State Park, Winchendon (Bacterial Exceedance)
Shannon Beach @ Upper Mystic, Winchester (Bacterial Exceedance)

Why are beaches closed in Massachusetts?

Bacteria in the water is usually attributed to stormwater runoff or sewage overflows after heavy rain, environmental experts say.

Swimming in bodies of water that exceed acceptable levels of bacteria can cause gastrointestinal illness, skin rashes and itching.