Revised rules proposed by the state Department of Natural Resources point in the right direction. With a minimum of tweaking by state lawmakers, the rules should be put into effect.

At stake is the risk to the environment, and to human health, when manure runs off farm fields and into streams, rivers and lakes.

Two pollution cases in Dane County in the winter of 2004-05 illustrated the problem. Manure polluted the west branch of the Sugar River near Mount Horeb, killing trout. Manure also polluted Dorn Creek just north of Lake Mendota.

In another case, in the spring of 2004, a family in Kewaunee County complained of illnesses they said were caused by pollution of their well water from manure spread on a nearby field.

Changes in federal environmental rules require Wisconsin to toughen its manure regulation of the state's largest farms - those with the equivalent of 700 milking cows, 2,500 pigs or 55,000 turkeys. Only about 150 of Wisconsin's 30,000 livestock farms are that large, but each of those large farms can produce as much waste as a city of 18,000 people.

Smaller farms are subject to local regulation. Dane County tightened its manure rules last year.

The DNR's plan requires all large farms by 2010 to do what most already do: strictly limit the spreading of manure on frozen or snow- covered ground. Frozen ground is one of the biggest reasons for manure runoff.

The plan also requires the regulated farms to have six months of liquid manure storage, which 80 percent of large farms already have, and it places other rules on manure management.

The plan provides the flexibility needed to reduce unintended consequences. For example, one result of limiting winter application of manure could be a flood (literally) of manure spreading in spring. The plan responds to that risk by allowing farmers to apply manure under certain conditions in the winter, if it is injected or incorporated into the ground.

The proposal also adds a streamlined permit process that could benefit many farmers.

The state Natural Resources Board approved the proposal. The next stop will be the Legislature, where Senate and Assembly committees could accept it, reject it, or recommend changes.

Some farm groups object to some of the provisions. Lawmakers should listen to ideas that would help to simplify the regulation.

For example, a ban on manure application when forecasts call for a 70 percent chance of rain may be unproductive, given how problematic forecasts can be and given the incentive farmers already have to be careful of rain.

But legislators should reject any major alterations. The plan should be an important part of Wisconsin's efforts to protect its water quality.