Dangerous rip currents were expected along the Maine coast from early Monday into the evening, according to a warning issued by the National Weather Service.

The coastal hazard message said there was a high risk of dangerous rip currents from 8 a.m. Monday through the evening in York, Cumberland, Sagadahoc, Lincoln and Knox counties.

“Rip currents can sweep even the best swimmers away from shore into deeper water,” the weather service statement said.

Lifeguards at some of the most popular beaches in Maine have been on high alert this summer as more swimmers need to be rescued after being pulled into rip currents. A series of high-water storms battered the shoreline last winter and reshaped the surf zone, creating a new system of largely invisible underwater troughs and sandbars.

Old Orchard Beach lifeguards have been especially busy rescuing swimmers caught in a newly formed rip current near the pier and others who step into a deep 6-foot trough formed between sandbars.

The Old Orchard Beach Fire Department posted a weather alert on Facebook about the dangerous rip currents expected Monday. Lifeguards were on the beach from 10 a.m. to 5 p.m.

The weather service is advising people to swim near a lifeguard. If they are caught in a rip current, swimmers should relax and float instead of trying to swim against the current. If they’re able, they can swim in the direction following the shoreline. If the swimmer cannot escape, they should face the shore and yell or wave for help, the weather service said.

The weather service also issued a small craft advisory for 4- to 7-foot seas in coastal waters from Port Clyde to the Merrimack River in Massachusetts. That advisory is in affect until 6 a.m. Tuesday.