A preliminary investigation shows "murky and cloudy" water in a public swimming pool helped conceal the body of a drowned Haitian woman for two days while people swam there, authorities said.

The Bristol County district attorney's office said the body of Marie Joseph was submerged at the bottom of the 3.6-metre deep end of the pool, in Fall River, Massachusetts, from Sunday afternoon until Tuesday night.

Joseph, 36, was a hotel housekeeper in Newport, Rhode Island. She was from Haiti and had five children. Her body was discovered after it floated to the surface shortly before some youngsters sneaked into the pool for a clandestine swim on Tuesday night.

The medical examiner's office has determined the manner of her death to be accidental and the cause to be asphyxiation by drowning.

The probe shows the water in the pool was murky from the time the pool opened for the season last Saturday. Visibility tests conducted on Wednesday revealed a diver couldn't be seen at a depth of up to 1.2 metres below the surface of the water.

"Although this office is releasing this preliminary information regarding the case today, the investigation into the death, the circumstances surrounding it and the delay in discovering the body is ongoing," the district attorney's office said in a statement.

The death at Veterans Memorial Pool, south of Boston, surprised and troubled swimmers, residents and public officials.

The Department of Conservation and Recreation, which runs the pool, immediately closed all 30 deep-water swimming pools and began reviewing safety and operational procedures.

Department of Conservation and Recreation Commissioner Edward Lambert said that 11 pools were set to reopen today after safety inspectors found they met all safety guidelines and their staff were well-trained.

Additional pools will reopen once their reviews are complete.

But Bristol County pool will not reopen anytime soon because its entire staff has been suspended. City officials also have said that they will not issue a permit to reopen until state officials assure them that swimmers will be safe there.