Just days before a decision on a pivotal issue for the Delaware River - whether to allow natural gas drilling in the watershed - the vote appears to be off.

The Delaware River Basin Commission, which oversees water use in the region, was poised to vote Monday on regulations that, if approved, as many expected, would have ended a drilling moratorium.

A "yes" vote would have opened several northeastern Pennsylvania counties to drilling. It would have made the river, which provides drinking water for 15 million people, including Philadelphia and some suburbs, vulnerable to its effects.

But now, the vote has been postponed, the Delaware Riverkeeper Network, an environmental group opposed to the drilling, has announced.

The organization was tipped off when the New Jersey State Police called to ask if they still wanted to keep their permit to protest outside the venue because the meeting had been canceled, said deputy director Tracy Carluccio.

Astonished, the network called basin commission officials, couldn't get a confirmation, but then called the Trenton facility where the vote was to be held and was told the meeting was off.

Commission officials could not be reached for comment, but a source close to the negotiations confirmed Thursday night that the meeting would be canceled.

Earlier in the day, Delaware Gov. Jack Markell had announced that his state's vote would be "no."

"Once hydrofracturing begins in the basin, the proverbial 'faucet' cannot be turned off, with any damage to our freshwater supplies likely requiring generations of effort to clean up. In this case, it is more important to get it right, than to be fast," Markell wrote in a letter to the other commission members.

Those members - Pennsylvania, New Jersey, and New York, all with land in the basin, and the federal government - have not announced their votes. While a 3-2 vote is sufficient, a unanimous vote would have shown strong bipartisan support for the regulations.

It was widely believed that Pennsylvania and New Jersey were likely to vote yes.

New York, which is still completing an environmental-impact statement and coming up with its own regulations, was expected to vote no.

Also, its attorney general has filed a federal lawsuit contending that the commission should have done its own environmental-impact statement. The commission had applied for and received U.S. House committee approval for $1 million to do the study, but it was never finalized.

Many were uncertain how the federal government would vote. The federal representative on the commission, the Army Corps of Engineers, gets input from more than a dozen agencies with an interest in drilling, but all with different perspectives. The National Park Service has urged caution. The Energy Department would likely support more domestic fuel.

Markell, a Democrat, wrote in his letter that the proposed regulations lack critical details on how public health and safety would be protected.

"By far, the single most important issue for a downstream state like Delaware is whether the wells are being drilled, constructed, and operated in a manner that adequately protects our public and private water supplies," he wrote.

He said the Delaware watershed is the primary water-supply source for at least two-thirds of Delaware's residents.

Markell said he believed that natural gas can be obtained without compromising the quality of the water supply. But regulating it in the watershed requires the "close coordination of multiple regulatory regimes," some of which had inadequate or unfinalized rules, he said.

"The governor's perspective is, 'Let's get a better sense of the regulations that would be in place were drilling to begin, rather than authorize drilling and keep our fingers crossed,' " said his chief strategy officer, Brian Selander.

The industry has been eager to gain access to the gas-rich Marcellus Shale formation underlying much of the Upper Delaware.

Late Thursday, Marcellus Shale Coalition spokesman Travis Windle said he could not comment on whether the Monday vote had been canceled.

"However," he said, "we remain hopeful that the DRBC will move forward with common sense regulations aimed at responsibly developing clean-burning, job-creating American natural gas in the region."

The proposed rules would have allowed some 300 natural gas wells to be permitted for starters, with thousands more likely to follow after a commission review at 18 months. The commission's lowest estimate is 4,800, but other groups say it could reach 18,000 or more.

Experts have said that no matter which way a vote went, litigation was all but certain.

The Riverkeeper Network, for one, indicated they intended to file for a federal injunction to prevent the rules from taking effect if the commission approved them.

Pennsylvania already has a lot of drilling - more than 4,000 wells so far in areas outside the Delaware basin - and the Republican governor, who received large campaign contributions from the gas industry, is business-friendly.

New Jersey, also led by a Republic governor, has no Marcellus Shale to speak of, but it has a hunger for cheap, domestic natural gas.

Earlier in the week, environmental groups had ramped up their public opposition, holding news conferences in all four states. They brought to the Philadelphia office of the Army Corps a box they said contained 73,910 letters and petition signatures objecting to drilling in the watershed.

On Wednesday, Josh Fox, producer of the anti-drilling film Gasland, and climate-change activist Bill McKibben of Vermont released a video aimed at bringing Vice President Biden into the debate and urging him to persuade his home state of Delaware to vote no.