Reports of a person in distress in the water at Cottonwood Lake at Hellyer County Park came in at about 1:40 p.m. and rescue crews headed to the scene.
Dive teams with the Sheriff's Office, the San Jose Fire Department and park rangers assisted in the recovery of the person's body following an apparent drowning. After a coordinated underwater search, the individual was found and pronounced dead at 4:11 p.m.
ABC7 Eyewitness News spoke with a fisherman who jumped into the water to try to save the man. He said he saw him go into the water with his hoodie and sweat pants still on.
"(He) was swimming and almost seemed like he was just taking a dip in there, but obviously,a little bit off being in the middle of this lake where people don't swim at. Once he kind of seemed to go underneath the water, I felt like I had to jump in and try to save him. But, at that point, he never kind of came back up," said Brandon Wilson.
It remains unclear why the individual entered the lake, the Sheriff's Office said. The person's identity has not yet been confirmed.
ABC7 Eyewitness News contributed to this report.