TRAVERSE CITY, Mich. — Crude oil that flows through twin pipelines beneath the channel linking Lakes Huron and Michigan could be transported to refineries in other ways, although the likelihood that the pipes will fail probably won't change much for the next several decades, according to a report released Monday.

The final version of an independent analysis commissioned by the state of Michigan lists six options for the future of Enbridge Inc.'s Line 5, which carries nearly 23 million gallons of oil and liquid natural gas daily between Superior, Wisconsin, and Sarnia, Ontario. The route includes part of Michigan's Upper Peninsula and a 5-mile-long segment beneath the Straits of Mackinac, where it divides into two 20-inch pipes.

Enbridge contends the underwater segment laid in 1953 is in good condition, while environmental groups, Native American tribes and other critics say it poses a high risk of leaking oil into an ecologically and economically vital waterway.

The study was conducted by the consulting firm Dynamic Risk of Calgary, Alberta. The alternatives it offers are similar to those in a draft released in June. They range from continuing Line 5's operations to shutting it down and transporting its oil through other pipeline networks, new lines in trenches or tunnels beneath the straits, or by rail, truck or barge.

While some opponents say other existing pipelines have enough capacity to handle Line 5's oil, the report says that's not feasible, despite keeping it on the list of options. It also says rail is the only realistic and "fully developed" non-pipeline alternative.

The analysis doesn't endorse any action but appears to support Enbridge's argument that Line 5's underwater pipes are sound, saying a "thorough assessment of all available information" suggests prospects of failure due to corrosion are small.

Critics disagree, noting the company's recent disclosures of spots where enamel coating has worn off and bare metal is exposed, which have drawn criticism from Gov. Rick Snyder and other state officials.

The report also says the only age-related threat to the pipes' integrity is from vibrations caused by powerful currents in the straits. Even so, it says, "time is a not a significant factor in the failure probability estimates" for the lines, projecting that the likelihood of failure will rise by about 0.4 percent between 2018 and 2053.

An opposition coalition called Oil and Water Don't Mix said the report does nothing to ease its worries.

"We have more than enough information to know this pipeline does not belong in the Great Lakes," coordinator Sean McBrearty said.

Beth Wallace, pipeline safety specialist for the National Wildlife Federation, said the study's findings are based on "standards written largely by industry or industry associations — a very low bar."

Enbridge spokesman Ryan Duffy said the report "reiterates the importance of Line 5 to the region," adding that the company would "work with the state of Michigan to ensure the safe operation" of the pipelines.

State agencies had no immediate reaction to the complex, 379-page analysis, but said they would take public comment for 30 days. Public feedback sessions were scheduled for Dec. 6 in Taylor, Dec. 12 in St. Ignace and Dec. 13 in Traverse City.

A separate study of risks posed by Line 5 is in the planning stages.