Thursday is expected to be the hottest day of the year so far for many in Massachusetts, with temperatures soaring into the 90s around Boston. If you're planning to beat the heat by heading to the beach, you'll want to check first to make sure your favorite swimming spot is open.

The Department of Public Health publishes a daily dashboard of beach closures in the state. On Thursday there were more than a dozen beaches closed for swimming due to bacteria levels or other reasons.

One notable entry on the list is Walden Pond's main beach, which is closed all summer because of construction work on a new bathhouse. 

Take a look below at today's beach closures, which was last updated at 9 a.m. Thursday.

Damon Pond Beach, (Bacterial Exceedance)
Walden Pond - Main, (Other)
Richard P. Sharon Beach, (Bacterial Exceedance)
Miacomet Pond, (Harmful Cyanobacteria Bloom)
Short Beach, (Bacterial Exceedance)
Collins Cove, (Bacterial Exceedance)
Juniper Point, (Bacterial Exceedance)
Steps Beach, (Other)
Peckham Pond at Cape Nihan, (Bacterial Exceedance)
Beamans Pond, (Bacterial Exceedance)
Pearl Hill Pond Beach, (Bacterial Exceedance)
Crow Hill Pond Beach, (Bacterial Exceedance)
Donovans Beach, (Bacterial Exceedance)
Halford Beach, (Bacterial Exceedance)

How does bacteria get in the water? According to health experts, it can enter through stormwater run-off, malfunctioning septic systems and sewer overflows, wildlife and pet waste or agricultural runoff. 

Swimming in water with unsafe bacteria levels can result in gastrointestinal or respiratory illness, as well as skin rash and itching. 

A recent report from Save The Harbor/Save The Bay declared that South Boston has some of the cleanest urban beaches in the country. 

Pleasure Beach and City Point got the highest marks, and Nantasket, M Street and Carson beaches also scored well. The report also said Wollaston Beach in Quincy continues to improve after upgrading their stormwater and sewer systems in recent years.