West Yorkshire Police confirmed this afternoon that teams searching for the 32-year-old had now found a man's body.
A spokesman said arrangements are being made to recover the body and specially trained officers were supporting his family.
The victim has not yet been named, but police said he was an Eastern European man from the Leeds area.
The search began last night at around 7pm when emergency services were called to reports of a man in difficulty the lagoon.
Superintendent Marianne Huison, of West Yorkshire Police, earlier said: "We are continuing inquiries at the scene of this tragic incident and, while the male has not yet been recovered, it is, at this time, believed he has sadly drowned.
"I would like to remind all residents in, and visitors to, West Yorkshire of the extreme dangers posed by swimming in or entering open water at lagoons or industrial sites."
The man is not the first to drown in the waters at the lagoon, which have claimed several lives.
Stuart Kemp, 19, drowned there in 1995 while swimming with friends.
And Bosnian-born student Denis Nadarevic, 16, drowned when he became trapped in a car which slid down a muddy bank into the water in 2004.