MANCHESTER — A man who was apparently drinking on the banks of the Merrimack River fell in the frigid water Saturday afternoon and drifted about 100 yards before his son could pull him to shore, police said.

The man, whose name was not released, was listed in serious condition at Catholic Medical Center, Manchester Police Sgt. Todd Boucher said.

Police were investigating how the man ended up in the frigid water, which carried him about 100 yards downstream before his son jumped in and got him to shore around 4 p.m.

District Fire Chief Al Poulin said someone at the scene was attempting CPR on the man when fire trucks and ambulances arrived.

Poulin said it was a challenge getting down the steep embankment, then pulling the man back up on a gurney as EMTs continued CPR before the man could be taken to the hospital. Police believe both men may have been homeless.