The sight of cows cooling off in a stream on a hot summer day used to be regarded as a harmless scene of pastoral farm life in Pennsylvania.

No longer.

Officials trying to clean up the Chesapeake Bay wince at the sight of cows polluting the water and damaging stream banks.

And state Rep. Mike Sturla now says it’s time state law bans cattle from Pennsylvania's waterways.

The Lancaster Democrat said he  is pushing for a bill that would make it unlawful for farmers to allow their cows to stand in streams. He plans to seek a legislator from Lancaster, York or Adams counties to sponsor the measure.

“We’re at a point where we’ve asked people nicely for 25 years,” he said.

“It’s about best management practices, and the dairy industry will tell you cows out of the water make for a healthier herd,” Sturla said. “Ultimately, it benefits the farmer as much as it benefits the stream.”

The idea comes as Pennsylvania faces growing pressure from federal officials to reduce its flow of sediment and nutrients into the Susquehanna River and into the bay.

Sturla, a member of the legislative delegation to the Chesapeake Bay Commission, said keeping cows from streams — a voluntary effort for the past 25 years — is an easy and effective way to make up ground.

Farmers generally support the cause but raised questions about how enforcement of such a law would be carried out.

“Having cows in the stream is pretty much your father’s practice,” said Steve Hershey, a dairy farmer from Manheim. “Cigarettes aren’t cool now like they were. Sitting your cows in the stream is not cool, either, anymore.”

Hershey, a member of the Lancaster Dairy Herd Improvement Association, had some concerns about specifics of such a law, but not its goal.

“It’s critical for the future of our county and the bay and agriculture’s image among the general public to keep them out of streams,” he said.

A spokesman for the Pennsylvania Farm Bureau said the organization wouldn’t comment on a cattle exclusion law until it could see the specifics of a bill.

It is unclear how many farmers would be impacted in Lancaster County.

Dennis Eby, a Plain sect outreach coordinator for the Lancaster County Conservation District, estimated that fewer than half of farmers with streams on their properties have taken steps such as streambank fencing to keep their cattle out of water.

Sturla said cutting off stream access would not place a financial burden on farmers because alternate water sources, such as watering troughs, exist now around the barnyard.

He said a law banning cows from standing in streams would allow cattle crossings of streams as part of common conservation practices such as streambank fencing.

“As a farmer, why wouldn’t I do that just for the safety of my own cows, the safety of the cows downstream and safety of anybody who gets close to that stream? Why would I want, basically, an open sewer?” Sturla asked.

Sturla said he is seeking a lawmaker who represents a large farm constituency to sponsor the bill because it would carry more weight in the House. Sturla’s district primarily covers Lancaster city.

As an indication of how far Pennsylvania has to yet to go in reducing runoff into streams, Sturla was among legislators from five states last week who visited a farm in West Lampeter Township as a model for stream cleanup. As the group pulled up, cows were lounging in a stream next door.

But Chesapeake Bay Commission members, meeting in Lancaster last week, made a point of citing a new $1.4 million matching grant awarded to Pennsylvania to be spent exclusively on measures to keep cattle out of streams in the Fishing Creek watershed in southern Lancaster County.

Among the partners in the project: Professional Dairy Managers of Pennsylvania, and the American Dairy Association North East.

“The science is pretty clear that having cows defecating in streams is not good for people or the cows. It creates real issues for both populations,” said Joe Sweeney, past chair of the Lancaster Farmland Trust.

Any cattle exclusion proposal would have to overcome a 1980 provision to the state’s Clean Streams Law that explicitly forbids the state or any local government from requiring a farmer or landowner to erect fences to keep livestock out of rivers and streams.