Republican Larry Hogan speaks at a gubernatorial forum in Ocean City on Saturay. (AP Photo/The Daily Times, Joe Lamberti)

Maryland Republican gubernatorial candidate Larry Hogan on Tuesday unveiled a new Web ad in which he vows he would clean up the Chesapeake Bay by getting tough on other states contributing to pollution in Maryland.

The ad is part of a stepped-up focus on the environment by Hogan’s campaign, which has largely been driven by economic issues, including promises of tax cuts, as he battles Lt. Gov. Anthony G. Brown, the Democratic nominee.

Hogan takes aim specifically at the Conowingo Dam, located in the northeastern corner of the state on the Susquehanna River. Hogan contends that sediment coming over the dam, including from long-neglected reservoirs, is among the biggest sources of pollution of the Bay — an issue that many environmentalists have said is overstated.

“The Army Corps of Engineers has sediment ponds up north of the Conowingo Dam that haven’t been cleaned out for decades,” Hogan says in the ad. “They have a role to play. And we’ve got to get the other states to pay their fair share. We’ve got to be tough, we’ve got to stand up for Marylanders, we’ve got to fight back against the federal government, and we’ve got to, if necessary, take these other states to court.”

Hogan has also criticized Brown this week for the diversion of funds from environmental programs to cover budget shortfalls during the administration of Gov. Martin O’Malley (D).

In response, Brown campaign manager Justin Schall sharply questioned Hogan’s commitment to the environment.

“If Larry Hogan is so interested in the environment, why does he openly question the science of climate change and oppose efforts to reduce storm-water pollution into the Bay?” Schall asked.

Hogan has ridiculed Maryland's storm-water pollution program, deriding its funding source as the “rain tax.” In a Republican debate in June, Hogan said it was a “scientific fact” that humans are contributing to climate change, but he said “the question is how much and what we can actually do to solve the problem.”

Schall also said that Brown, rather than Hogan, has the support of environmental groups such as the Sierra Club and the League of Conservation Voters because “Hogan’s Republican ideas on the environment ... would take Maryland backwards and put the Chesapeake at risk.”