State officials are again restricting open-water swimming at one of the region’s most popular recreational bodies of water.

But at least on Sunday, the first day this season that the swimming rules went back into effect at Walden Pond, the Herald spotted some swimmers defying the policy and traversing the 1/2-mile oasis in Concord.

Walden Pond State Reservation on Saturday announced that last year’s open-water swimming rules would return, effective Sunday. That means swimming is not allowed outside the area designated by ropes and buoys from 10 a.m. to 6 p.m. while lifeguards are on duty.

The Massachusetts Department of Conservation and Recreation handed down open-water swimming rules at Walden Pond last July in the wake of a series of drownings across the state.

Open-water swimming is only allowed during park operating hours when lifeguards are not on duty, DCR said in a statement, stressing the policy helps ensure that lifeguards keep their focus on designated swim areas inside the ropes and buoys. The allowed open-water swimming hours are from 5 to 10 a.m. and then from 6 to 7:30 p.m.

Also, open-water swimmers must have a brightly colored swim buoy — a flotation device that’s attached to swimmers via a strap and helps increase their visibility.

“Walden Pond is over 100 feet deep in areas and a half-mile in length,” DCR said. “All swimmers, but especially Open Water Swimmers, should recognize that swimming distances in deep water is inherently dangerous and may exceed a swimmer’s physical and psychological limits. Open water swimming is a challenging endurance sport and should never be attempted by individuals who have not trained for or prepared for the activity.”

Last summer, amid a spike of drownings across Massachusetts, DCR initially implemented a full open-water swimming ban at Walden Pond.

That ban led to outrage among the open-water swimming community. Swimming enthusiasts wrote letters to the state and more than 10,000 signed an online petition to amend the ban. Also, dozens of legislators sent a letter to the DCR commissioner and Gov. Charlie Baker, asking that the ban get lifted.

Ahead of this summer, DCR is continuing to recruit lifeguards. The state increased the hourly rate for lifeguards to between $21 and $26 depending on position and associated certifications; last year’s starting rates were $20 for lifeguards and $21 for head lifeguards. The agency is also offering a $500 retention bonus for lifeguards who continue to work through the end of the season.

“We want visitors to our designated swimming areas to have fun while cooling off from the summer heat, but we also want to stress safety and the importance of taking precautions to keep yourself and your family safe this summer,” said Acting DCR Commissioner Stephanie Cooper. “Our lifeguards are a valuable resource, but we also count on the public to take an active role in watching their children when they are in the water, using caution when swimming at unguarded beaches, and utilizing safe swimming practices to avoid a tragedy.”