TRAVERSE CITY, Mich. — Michigan Gov. Rick Snyder said Wednesday that twin oil pipelines in a waterway linking two of the Great Lakes appear to have sustained minor damage from a vessel that may also have caused a recent leak of coolant fluid from electric cables.

Enbridge Inc.'s Line 5 runs along the bottom of the Straits of Mackinac in the vicinity of the American Transmission Co. power cables that released an estimated 600 gallons (2,270 liters) of insulation fluids earlier this month.

Enbridge notified state officials Tuesday that inspections after the leak was discovered turned up two small, previously unseen dents in one of its pipelines and a single dent in the other.

"A review of all leak detection systems and available data indicates the structural integrity of the pipelines has not been compromised," spokesman Ryan Duffy said, adding that the company would make repairs.

Snyder said in a news release that an anchor strike "was the largest risk identified in a previous independent analysis of the Enbridge pipeline, which is apparently what happened in the Straits last week. We need the right answers, but we need them as soon as we can get them so that we can take action faster to protect the Great Lakes."

The U.S. Coast Guard, which is leading the investigation, has said "vessel activity" might have caused the leak from the power cables. It has not identified a suspect or said whether a dropped anchor was responsible.

Snyder spokesman Ari Adler said the governor was referring generally to the danger posed by anchors and had no specific knowledge of the culprit in this case.

Lt. Gov Brian Calley, acting on Snyder's behalf because the Republican governor is traveling out of state, sent a letter to state Attorney General Bill Schuette requesting legal action against the presumed vessel's owners, operators and "other potential responsible parties."

"There is no excuse for the ship's actions, which risked devastating environmental harm as well as the loss of vital infrastructure for communications, electrical power and heat for residents of the Upper Peninsula," Calley said.

Schuette said his office is determining what legal steps might be appropriate.

The 5-mile-wide (8-kilometer-wide) waterway, which connects Lake Huron and Lake Michigan, is used heavily by ships that haul iron ore, coal, limestone and other bulk cargo, and by recreational boats.

Line 5 carries about 23 million gallons (87 million liters) of crude oil daily between Superior, Wisconsin, and Sarnia, Ontario. The underwater segment that traverses the Straits of Mackinac is divided into two side-by-side lines.

Environmental groups contend that the segment, which was laid in 1953, is a spill hazard and should be decommissioned. The company says it's in good shape and could operate indefinitely.

Enbridge is studying alternatives for the segment's future under an agreement with the state of Michigan, which owns the lakebed and granted an easement allowing the pipelines to go there. Among the options is replacing the pipelines with new ones that would be placed in a trench or tunnel. Enbridge is also studying ways to prevent anchor strikes of the existing lines.

The company agreed to report by June. Snyder said the latest development shows a need to finish the studies "as soon as feasibly and responsibly possible."

He said he would order the company to decommission the lines if studies find that a tunnel for replacements could be built beneath the lakebed without causing significant environmental damage.

Environmentalists say the only responsible solution is to route Enbridge's oil elsewhere, not tunnel under the waterway.

"Pipelines do not belong in the Straits of Mackinac, period," said Sean McBreaty, coordinator of a coalition called Oil and Water Don't Mix. "Our state's economy, tourism, and way of life revolve around keeping our Great Lakes in a pristine condition."

The Coast Guard said it would use thermal scanning technology and a remotely operated underwater vehicle to get a better look at the damaged utility cables and develop salvaging plans. A contractor is continuing to vacuum the remaining insulation fluid — a type of mineral oil that contains benzene — from the disabled lines.

Surveys by boat and aircraft have produced no sightings of pollution from the leaks, federal and state agencies said in a statement. It added that wildlife biologists have observed more than 3,000 waterfowl in the area and seen no abnormal behavior.