Rescue workers will resume their search on Monday morning for Dariusz Czarnota, 37, of East Hampton.
On Sunday afternoon, he jumped off a dock at the Pattaconk Yacht Club in Chester into the Connecticut River and was swimming to his brother's boat when he went underwater.
Grybowski said Czarnota and his brother would usually come up the river from Old Saybrook every weekend and knew these waters well, but the current was too strong.
Authorities said two currents come together at the location, making this a dangerous place to swim.
"The currents tend to swirl and drag you under in this area, so you have to be really careful when you're swimming," James Grzybowski, deputy chief of the Chester fire department, said.
State Police divers and local authorities are investigating this as a possible drowning, Lt. Paul Vance, a spokesman for Connecticut State Police, said.
Czarnota went underwater around 2 p.m. while swimming. The search will continue for the foreseeable future, according to state police.
"The state police and our boat will be doing a search of the river using sonar to try and locate exactly where he is at this time in the water" Grzybowski said.
