Plans for a commuter ferry on the Yarra have hit an early snag, with Rowing Victoria warning it could cause crashes, capsize smaller boats and even make the the river too dangerous for Olympic training.

Rowing Victoria has raised alarm about the proposal from Port Phillip Ferries and developer Caydon Property Group to run a commuter ferry from Chapel Street to Docklands via the Yarra.

Chief executive Nick Gall said the river was already congested with as many as 4000 rowers a day leaving the boathouses near the Princes Bridge during the proposed ferry's morning peak, between 5.30 and 8.30.

"There are a massive, massive number of people heading down the river at that time of day," Mr Gall said.