A BBC analysis suggests 195 out of 402 official bathing waters are patrolled between July and September.
The National Water Safety Forum said it was "impractical" for every beach to be covered.
The absence of lifeguards was raised as a concern after the deaths of seven men at Camber Sands in 2016 but an inquest concluded they may have drowned anyway.
There is no formal list of which beaches have lifeguards as the Royal National Lifeboat Institute (RNLI) only publishes details of the ones it patrols. Local councils and private land owners provide others.
Seven people died in two incidents at Camber Sands in East Sussex in summer 2016.
The families of five men, who died in the second incident in August, described the victims as physically fit and competent swimmers.
An inquest into the deaths, which concluded in June 2017, heard the RNLI had recommended that Rother District Council employ lifeguards after a risk assessment in 2013.
The inquest was also told the RNLI then rejected a request to put lifeguards on Camber Sands 16 days before the August deaths, citing a lack of resources.
Lifeguards now patrol the beach. However, the inquest concluded that the men may still have drowned even if there had been lifeguards.
490
in 2016
215
suspected accidents or natural causes, almost half of which were between June and September
163 males died in accidents or by natural causes
32 females
67 by a coast, shore or beach
RNLI lifeguards rescued 2,082 people across the UK and Jersey, and saved 127 lives, in 2016.
The charity, which lists the beaches it patrols on its website, said it worked with councils and other beach owners to determine lifeguard cover.
"There may be times when we will approach a local authority or beach owner if there has been something that has happened on that beach, but the majority of times it will be due to the local authority or beach owner coming to us", a spokeswoman said.
The RNLI said it would not be possible to put lifeguards on to all bathing waters and services "need to be judged on a needs basis as opposed to a cost implication".
The cost to train a RNLI lifeguard is Â£712 plus a further Â£812 for equipment.
The water safety forum said some of the beaches not covered by lifeguards may not attract significant numbers of people or pose a significant risk.
"Water-related accidents occur on inland waters as well - it's very important that this is not forgotten," a spokeswoman said.
Seeing children swimming and jumping off rocks into the sea, Alexa Mullane was concerned that there were no lifeguards at Durdle Door beach in Dorset.
The managing director of a health supplements company visited the beach, as well as Lulworth Cove and Studland with her family, including two baby nieces - during the good weather in June.
She saw "lots of kids swimming quite far out and also jumping off really high rocks into the sea".
"I definitely thought that it wasn't safe," Ms Mullane said. "You could see the rocks under the water and it was scary to see them jumping from so high into the water."
James Weld, whose family owns Lulworth Estate which owns Durdle Door, responded: "The signage makes it very clear that people should not jump or 'tombstone' from Durdle Door because of the serious risk of injury.
"Like many beaches in the UK we do not have lifeguards on duty, our coastal safety signs clearly advise all visitors of this fact.
Mr Weld added that beach wardens and rangers, who are not trained lifeguards or first-aiders, patrol Lulworth Estate's beaches regularly.
BBC England's data unit analysed a list of beaches patrolled by lifeguards, RNLI and otherwise, using data provided by the RNLI, the Beach Guide and local councils' websites, as of 7 July 2017.
The list was compared to the Department of Environment Food and Rural Affairs' list of designated bathing waters in England, with inland waters - such as Lake Windermere and Hampstead Heath in London - stripped out.
Explore the data here.
Just over half of bathing spots along England's coast have no lifeguards on duty over the summer.