A new report states that voluntary measures to protect the Great Lakes from farm manure have proven insufficient.
As a result, the draft report by the International Joint Commission says Canada and the U.S. should look at legislation.
The runoff is especially acute in Lake Erie, where out-of-control algae growth has created dead zones.
The report says phosphorus in animal waste from intensive livestock operations plays a big role in the deveopment of the algae.
The draft also criticizes the governments' lack of progress in identifying chemicals harmful to the lakes and an absence of strategies for dealing with them.
With files from the Canadian Press