A Long Island birthday party for pals from the prestigious Rochester Institute of Technology turned tragic today when one celebrant drowned in a backyard pool.

Nelson Cole, 21, of Boerum Hill, Brooklyn, was one of nine friends who were celebrating Jeffrey Soto’s 22nd birthday Saturday at his Plainfield home, said Nassau Police Det. Sgt. Daniel Ayrovainen.

After going in and out of a backyard pool all day and night, two pals at 4 a.m. noticed Cole was laying motionless at the bottom of the 8-foot, deep end.

The friends pulled him from the water, and performed CPR — but it was too late: Cole was pronounced dead at 5:09 a.m. at North Shore-LIJ Plainview.

Soto was given a desk appearance ticket because alcohol was served to a 20-year-old male at the party. Cops were investigating what role alcohol may have played in the tragedy.