Southern River is an electoral district of the Legislative Assembly in the state of Western Australia.

The redistribution ahead of the 2005 state election shifted Southern River eastward, making the seat safer for the Labor Party.

That election saw Paul Andrews defeat Monica Holmes a second time, with a much wider margin in large part due to the redistribution changes.

The next redistribution saw much of the previous changes reversed, making Southern River once again a marginal seat.

With Labor's hold on the seat now much more tenuous, Andrews was defeated at the 2008 state election by Liberal candidate Peter Abetz.