Various safety failures by pipeline company Enbridge Inc. (ENB) and "weak regulation" by U.S. government officials are to blame for the July 2010 spill of nearly 20,000 barrels of oil into Michigan's Kalamazoo River, the U.S.'s lead transportation regulator said Tuesday.

Poorly trained staff in Enbridge's control room, an uninformed public and mistakes made during the first hours of the response caused oil to flow from Enbridge's Line 6B pipeline near Marshall, Michigan for 17 hours after the rupture, according to the findings from the National Transportation Safety Board's investigation into the spill.

Calgary, Alberta-based Enbridge acted like "Keystone Cops," making "multiple mistakes and missteps" in its response to the spill, NTSB Chairwoman Deborah Hersman said during a public review of the board's findings.

Also coming under criticism were the U.S. Pipeline Hazardous Materials and Safety Administration, for what the NTSB called "weak regulation for sensing and repairing crack indications," as well as local firefighting personnel, which the board said weren't adequately trained to respond to the initial public reports of odors from the spill.

In July 2010, oil spilled from Enbridge's Line 6B pipeline in Michigan, flowed into a nearby creek and then into Michigan's major waterway, the Kalamazoo River. It was one of the worst oil spills ever in the U.S. Midwest, which is a crossroads for pipelines carrying oil from producers in Canada. Enbridge, which had $19.40 billion Canadian dollars (US$19.05 billion) in revenue last year, has seen a total of US$765 million in expenses related to the spill.

The board issued 19 recommendations to government, industry and emergency personnel groups to improve pipeline safety and spill-response standards, and called for the creation of a set of federal standards for oil-spill response planning.

Results of the board investigation, released Tuesday, found that staff in Enbridge's control room failed to recognize the spill, leading them to try to restart the pipeline twice, which increased the amount spilled.

Local firefighters also didn't immediately contact Enbridge when they detected the spill, which would have reduced the amount spilled, the NTSB said. However, they also laid part of the blame for that on Enbridge, saying it should have trained local first responders on how to deal with pipeline spills.

PHMSA, in charge of pipeline safety, also failed to follow up on signs of corrosion cracking in the Line 6B pipeline that they found in previous investigations, the board said.

In a statement, Enbridge said it's already made changes to improve its control room operations and to enhance its spill prevention, detection and response programs. It said it would review the NTSB's findings to see if "further adjustments are appropriate."

"We believe that the experienced personnel involved in the decisions made at the time of the release were trying to do the right thing," Enbridge Chief Executive Pat Daniel said in the statement. He added that the Kalamazoo River was re-opened for recreational use last month and that wildlife has returned to the spill area.

Write to Edward Welsch at edward.welsch@dowjones.com