The state Department of Environmental Protection has reversed a decision it made just weeks ago, abandoning a policy environmentalists said threatened all the state's rivers.

Gov. Deval Patrick announced the move in a conference call yesterday afternoon during which he gently took the agency to task for making a decision without informing him.

At issue was the definition of "safe yield," the total amount that can be pumped out of any water supply without causing "unreasonable" harm.

Last month, the DEP contended it had calculated safe yields for all 27 water basins in the state, and now defined it as the amount of water that would be present in them during a year of drought. In the case of the Ipswich River, that amounted to 21 million gallons a day more than communities are currently permitted to withdraw.

That pronouncement drew the ire of four environmental groups, including the Ipswich River Watershed Association, which were serving as a council of advisers to the agency, to withdraw from the council. Watershed association Executive Director Kerry Mackin said at the time the new safe yield definition took no account of the environmental damage the interpretation would cause.

"I'm happy to announce these important groups are back with us," Patrick said yesterday.

He went on to say the DEP has "suspended" its definition of safe yield and is forming a special panel that will be given one year to come up with a definition "that embraces environmental factors," Patrick said.

A sustainable water resources advisory committee that will include environmental agencies will team up with the Water Management Act Advisory Committee and the Water Resources Commission. The committee will provide advice to the DEP about a host of water issues, including a definition of safe yield.

Peter Shelley, speaking for the Conservation Law Foundation, said the environmental groups and the DEP "have been through a bit of a rough patch," but now look forward to cooperating.

"We have the very big challenge of restoring the health of all the commonwealth's rivers," Shelley said.

"It's the common goal we all have," Patrick said. "We have differences in how to achieve it."

Safe yield has been a bone of contention since the enactment of the state's Water Management Act in 1986. Asked how what hasn't been accomplished in 23 years could possibly be done in a year, Bob Zimmerman, executive director of the Charles River Watershed Association, said, "Because we've all agreed we have to. We have the science, we just haven't applied it."

The DEP apparently issued its initial definition of safe yield without input from the governor, who said he learned of it in a newspaper account.

"I expect them to give me a letter before they give it to you," Patrick said, referring to the members of the media taking part in the conference call.

In April 2003, the Ipswich River was named the third most endangered in the country by American Rivers, a national conservation group. The group cited excessive water withdrawals, particularly in the summer, as a cause for the designation.

Fifteen communities, stretching from Wilmington to Salem, depend on the Ipswich River watershed — which has at times been littered with dead fish on a dry riverbed — for either part or all of their water needs.