ANNAPOLIS, Md. (AP) — Scores of environmentalists gathered Thursday night in Annapolis to protest a "Potomac Pipeline," citing inaction on the part of the state in properly vetting the environmental impact of a project that would transport fracked natural gas under the Potomac River.

Protesters focused on the review process. The state, they said, has not conducted a thorough enough review.

Maryland must decide by March 15 whether it will accept an offer by Canadian energy infrastructure company TransCanada to drill a pipeline that would transport fracked natural gas from Pennsylvania through approximately three miles of Western Maryland into West Virginia.

The project would involve drilling horizontally underneath the river. There are already 23 pipelines that cross the Potomac, according to the Maryland Department of the Environment.

Also on Thursday, Maryland Secretary of the Environment Ben Grumbles submitted a letter to the Baltimore District of the U.S. Army Corps of Engineers acknowledging that "the public has raised some concerns about the impact of" the Eastern Panhandle Expansion Project "on the environment and public health."

His letter also instructed Corps of Engineers to halt its review of the application until the state's Department of the Environment concludes its review.

Too little, too late, as far as some protesters were concerned.

"He's making like he's just heard of" public outcry, said Ann Bristow of Garrett County — Maryland's westernmost jurisdiction. But he's been made aware of it on multiple occasions, she said.

Grumbles told Capital News Service on Tuesday that the state is conducting a "robust review," and is "absolutely committed" to protecting the environment.

"Any pipeline that's built in the state is subject to stringent regulation and safeguards," Grumbles said. "We're in the process of developing safeguards and review" for the Potomac Pipeline.

A marching, Maryland-flag-toting bagpiper played "Scotland the Brave," as crowds of protesters encircled Gov. Larry Hogan's mansion Thursday evening, jeering "Don't take the bribe! No Potomac Pipeline!"

"Now that (Hogan is) threatening our homes," said Brook Harper, Maryland policy director for Chesapeake Climate Action Network, at the rally Thursday, "I think it's time we surround his."

The group was largely bused in from Western Maryland and from West Virginia.

Protesters sent a clear message: The environmental and health risks of the pipeline outweigh the potential benefits — which many in attendance said they were uncertain of.

"We need to leave our rivers alone," said Matt Seubert of Frederick, Maryland. "They've suffered so much damage over the years, we need to be restoring them instead of destroying them or digging under them."

Seubert added: "Clean water is the 21st century's oil. We can't play games with it."

The protest followed a teleconference Tuesday, during which legislators and environmental organization leaders accused Hogan of keeping the public in the dark throughout negotiations with energy company TransCanada and potentially undermining the drinking water supply of roughly 6 million in the Washington area.

Grumbles tuned in to the teleconference and was "really disappointed by the extreme" nature of the conversation, he told Capital News Service.

Grumbles called the conference "political and premature" and said their "basic viewpoint is that if you ban fracking you have to ban the use of natural gas infrastructure."

But, he said, "natural gas is a bridge fuel to cleaner energy."

Protesters disagreed, arguing that the administration should instead focus its resources on clean and renewable energy.

Last year, Maryland increased its renewable energy portfolio goals to 25 percent by 2020.

Protesters had mixed suggestions on how to remedy energy pollution as the state moves toward more renewable sources.

"I think that 'bridge fuel' should be" nuclear energy, said Karen Russell of Knoxville, Maryland.

"We should be putting our focus on solar energy," said Judy Stone of Cumberland, Maryland. "Because it's clean and the best long-term solution."

Legislators and environmental leaders said that considering TransCanada's offer is hypocritical because in 2017 the Republican governor signed a bill that banned fracking in the state.

But Grumbles said the governor was being criticized "for supporting responsible natural gas infrastructure" and that the administration "has demonstrated strong commitment to climate progress and environmental issues."

More than 44 percent of Maryland households use natural gas as their primary heating source, according to a 2015 Towson University study.

That number could also increase because, according to the same study, natural gas is more cost effective than traditional heating alternatives.

On average households using natural gas could save $806 more than households using heating oil, $1,172 more than those using electricity and $1,705 more than those using propane, the Towson study shows.

Grumbles on Tuesday also addressed concerns that committing to natural gas infrastructure could jeopardize meeting the state's climate goals.

Maryland needs "an array of tools and strategies to reach its climate goals," Grumbles said.

And natural gas infrastructure at "the right place and right time makes a lot of sense, with the appropriate protections," he said. "It's irresponsible to say we should be banning (it)."