Lincolnshire Police arrested three people on suspicion of murder after a body was found at a pumping station in Boston.
Two men, aged 26 and 33, as well as a woman, 26 were arrested in Boston last night and all three remain in custody as of Thursday morning.
Police named 46-year-old Polish national Marcin Stolarek as the victim after a body was found near Chain Bridge Road on the evening of January 12.
It is believed he died as a result of a sustained assault and his body was then disposed of in the waterway.
Officials at the Lincolnshire force have said significant resources have been dedicated to the investigation.
They are now appealing for anyone who has seen Marcin in the last four months, or who has information that could help the investigation, to come forward.
Detective Chief Inspector Karl Whiffen, from the East Midlands Special Operations Unit said: “I am appealing for anyone with information about Marcin to get in touch.
“Marcin lived in Boston but also had links to Spalding, and people in those communities may have details that could prove crucial to our investigation.
“Please come forward with information so that we can bring his killer, or killers, to justice.”
Anyone with information can call Lincolnshire Police on 101 quoting incident 313 of January 12.