SACRAMENTO  (AP) — The Central Valley Regional Water Quality Control Board will begin inspecting illegal marijuana grows across Northern California, reversing an earlier ban designed to protect employees

Last week the water board directed staff to join law enforcement in the field and write citations for environmental violations when appropriate.

Law enforcement agencies across the board's 37-county region had sought the help of water scientists so they could prosecute growers who flatten hilltops, divert streams or cause sediment to run into waterways. Growers often are not held to the same standards as traditional farmers.

"The environmental impacts are significant," Pamela Creedon, the board's executive officer, told the Sacramento Bee. "If we don't get some kind of control over this, we're going to have some serious damage being done."

Marijuana is the state's biggest cash crop with an estimated $14 billion in legal and illegal sales annually.

The state's nine regional water boards are quasi-independent agencies that set their own policies, though all are charged with enforcing the federal Clean Water Act and its California equivalent. The Central Valley board, which focuses on runoff from farming, construction and hundreds of dairies, did not previously have a policy for investigating violations associated with marijuana grows.

Yet its sister agency, the North Coast Regional Water Quality Control Board, aggressively seeks out and prosecutes growers who flatten remote hilltops, dam streams to divert water and allow sediment and chemicals to reach waterways. In 2007, that agency joined an environmental crimes task force made up of county district attorneys and code enforcement agents.

The change of policy also is being considered by the state's other regional boards after Assemblyman Dan Logue of Butte County protested that a state agency was refusing to enforce state laws.