A man died after tumbling into the Russian River before dawn Sunday, although it wasn't immediately clear if he jumped or fell, fire officials said.

Several transients in the area heard someone crashing through the brush near Moscow Road at about 2 a.m. followed by a big splash, Monte Rio Fire Chief Steve Baxman said.

Some of them ran down to the river to search for a person in the water and a man on the bridge ran to the fire chief's house and pounded on the door, Baxman said. Another person called 911.

The bystanders had found the man and pulled him out of the water when Baxman arrived. They performed CPR but the man couldn't be revived, he said.

Baxman said he believed the man who died was a 35-year-old transient fairly new to the area.

An autopsy will determine precisely how the man died.