NARRAGANSETT — Clear skies, brilliant sunshine and 90-degree weather — the perfect beach day.

But not for those who got a late start.

Throngs of sun seekers driving to and from Rhode Island’s most coveted coastal spots yesterday caused traffic jams on major roads and even on side streets, leading to an unprecedented move by the Department of Environmental Management by mid-afternoon: closing all state beaches to more comers.

“It’s for safety reasons,” the DEM’s Lt. Dean Lees said, “If there were an emergency, we couldn’t get EMS down there.”

For awhile, would-be beach goers, stuck in traffic, thought they had more to worry about than gridlock.

At first, the Department of Transportation message flashed on the Amber Alert signs over major highways read simply: ALL RHODE ISLAND STATE BEACHES CLOSED.

This prompted the phones to start ringing at the DEM, with callers asking if the closure was due to pollution.

“I can see how some people might have thought that,” Lees said.

Within a half-hour, the DEM had its message updated to say lack of parking was the problem.

The DEM yesterday was unable to provide precise attendance figures at the state beaches. But with temperatures today again expected to hit 90 degrees – yesterday’s official high at T.F. Green Airport – it likely that many again will be seeking relief from the heat.

The Narragansett police yesterday first alerted the DEM to the congestion problem, asking for temporary relief for their backed-up roads. Just before 2 p.m., when the decision to close the beaches was made, the beaches at Galilee were full, traffic was at a stop along parts of Sand Hill Cove Road, and the police directed traffic past full lots.

At first, DEM officials decided to let more cars enter the lots only after 50 cars left, helping to stagger traffic on the roads coming to and from the beach.

But after calling other towns along the coast — North Kingstown, South Kingstown, Westerly — the DEM found they were all having the same problems, Lees said. The decision was made to close them all for the rest of the day.

At 6 in the evening, staff at East Matunuck beach in South Kingstown would typically be on their way home. Not yesterday.

“This is definitely the busiest we’ve been so far this year,” supervisor Jackie Brouth said from the beach tower. “The fact that we’re staying until 7 says enough.” They had to stay open because too many people were still in the water to send the lifeguards home.

Yesterday was the first time that overwhelming traffic led to the decision to close all of the state beaches at once and for the rest of the day.

Closing yesterday afternoon wasn’t enough to slow things down at Misquamicut State beach in Westerly.

Just after 6 p.m., Meredith Barrett said she could only describe the scene as “really, really, really” busy.

“We’re in a crunch,” she said, raising her voice over the sounds of the early evening beachgoers to add, “I’m too busy to be interviewed.”

bjeffers@projo.com