Marijuana is illegal under federal law, but allowed for medicinal use under California and Oregon state law.
In California, marijuana (legal and illegal) amounts to the state's biggest cash crop.
Legal farmers who grow other crops are subject to environmental regulations.
But it's been tricky, and sometimes dangerous, for regulators to approach marijuana growers for the damage they do to streams.
The Central Valley Regional Water Quality Control Board recently decided to inspect illegal marijuana grows and hand out citations when violations are found.