Northcott Mouth, near Bude in Cornwall, is a quiet beach and was this year patrolled by lifeguards between July 7 and September 2, the day before local schools reopened, the RNLI said.
It is thought the woman, believed to have been in her 50s, went into the water at the remote beach to rescue her sons, aged 11 and 13, who had got into difficulty around 2pm on Monday.
Steve Instance, the RNLI lifeguard inspector, said Northcott is a quiet rural beach designated for peak-season lifeguard coverage only.
“Lifeguards patrol there in July and August through to the first week of September when local schools go back. Sunday was the end of the season for that beach,” he said.
“It is just unfortunate they have chosen to visit this beach the day after the lifeguards finished for the year. It is a quiet beach.”
The RNLI, which equips and trains the lifeguards, said that levels of coverage at specific beaches were recommended by the charity after it carried out a risk assessment, but decided upon by the local authority or the owners of private beaches, who pay their wages.
Information on the locations, dates and times of local lifeguard cover is displayed in the area.
Mr Instance said four other local beaches, which have more visitors, have lifeguards on duty further into September.
Because all the local beaches are linked at low tide, lifeguards from Crooklets beach, 1.5 miles away in the centre of Bude, raced to the scene in a 4x4 as soon as the alarm was raised, Mr Instance said.
The woman, whose identity has not been revealed, and her children where the only people in the water at the beach when the tragedy occurred, he added.
“We believe that the woman had gone in to rescue the boys,” he said.
“One of the boys got to the shore and the other was still in the water in difficulty. Two members of the public had also gone in.”
A member of the public raised the alarm after one of the boys made it back to shore. The other was rescued by the RNLI’s Bude inshore lifeboat.
Martin Bidmead, watch officer at Falmouth coastguard, said the mother was plucked from the water. Medics performed CPR before she was taken to North Devon District Hospital, Barnstaple, by rescue helicopter, he added.
There were emotional scenes yesterday as the family and friends of a four-year-old boy who drowned after slipping from a jetty arrived for his church funeral.
Dylan Cecil was on holiday visiting his grandparents when he fell into the water at Burnham-on-Sea in Somerset on Sunday, August 19. He was said to have been trying to get a closer look at the sea when the tragedy happened.
The youngster, from Kettering in Northamptonshire, disappeared from view while members of his family were enjoying a day on the coast.
His parents, Rachel McCollum and Darren Cecil, attempted to save him, while emergency services quickly launched a search and rescue operation.
His body was found by a member of the public four days later – and less than half a mile away from where he was last seen – at a nearby sailing club.
At St Mary’s Church in Kettering yesterday hundreds of mourners turned out to pay their last respects to the youngster, many wearing blue in honour of Dylan’s beloved Kettering Town FC and Sonic the hedgehog.
Mr Cecil was one of the pall-bearers for his son’s blue coffin, which also had a picture of Sonic on the side and a football scarf draped over it.