The mother of TV actress Nida "Tangmo" Patcharaveerapong says she does not believe that her daughter's death was the result of an accidental fall from a speedboat on the Chao Phraya River.

Rescuers found the 37-year-old actress's body in the Chao Phraya near the Pibul Songkhram 1 pier in Nonthaburi around 1.10pm on Saturday, about one kilometre away from where she fell from the speedboat around 10pm on Thursday night.

Tangmo's mother, Panida Sirayutthayothin, said she wanted to know who arranged the photoshoot her daughter was supposedly hired to do. She added it was difficult to believe that the six people, including Tangmo and her manager, were in the boat together just to have a meal. Looking at the photos, she said the actress appeared to have dressed up.

Ms Panida said people in the boat may have had an argument. One photo released of her daughter showed her looking unhappy as she sat alone at the back of the boat.

Ms Panida also discounted reports the toilet on the boat was not working properly. "Tangmo was a star. It's hard to imagine her going to the rear of the boat for that," said Ms Panida. Earlier reports said the actress went to the back of the boat to relieve herself, due to the boat's toilet being broken.

A speedboat passenger Wisapat "Sand" Manomairat said on Sunday she was looking at her mobile phone while Tangmo held on to her legs at the rear of the boat before slipping into the river.

Tangmo's manager said she was gazing at the river when the accident happened. She said the boat trip was only for sightseeing among friends.

Tangmo had not wanted to wear a life jacket because she wanted to pose for photos on the boat, she added.

A rescue worker on the search team said there was a deep cut on Tangmo's thigh.

The owner and driver of the speedboat have been charged with negligence and operating an unauthorised vessel.

A police source said the result of the post-mortem examination was expected late on Sunday.