Toxic chemical waste has been washed into the Yarra River at Warrandyte by Parks Victoria staff, killing trees and creating a "public health risk" near a popular Melbourne swimming spot.

According to a confidential internal report on Parks Victoria operations, a toxic cocktail of chemicals and herbicides has flowed into the Yarra from a "wash-down facility" near Pound Bend, which is a popular spot for swimming, fishing and canoeing inside Warrandyte State Park.

Siblings Oscar, 7, Sophie, 11 and Harry, 9, enjoying a swim at the Pound Bend Reserve in Warrandyte. Credit:Luis Ascui

An incident and hazard summary report, dated October 29, reveals the concrete site is used to "pressure-wash vehicles, triple rinse chemical containers and mix herbicides for use in the park".

But the area drains directly into the Yarra, and the report states that chemical waste from the depot's wash-down area has already killed a number of trees before entering the river.