Water police responded to reports of an overturned boat in the water near Jindalee, around 40km from the CBD, about 7am local time (9am AEDT).
St John Ambulance WA confirmed to 9news.com.au a man aged in his 70s was taken to Joondalup Health Campus with minor injuries.
He remains in a stable condition.
A second man, also aged in his 70s, is still being assisted at the scene.
He is understood to be in a critical condition.
A rescue helicopter landed in Mindarie to assist in the operation.
Police and emergency workers remain at the scene near a boat ramp at Mindarie Keys.
