ST. LOUIS -- A tourist boat was on the lake despite wind speeds far exceeding allowable limits when it sank last month in Missouri, killing 17 people, according to a certificate of inspection made public Wednesday.

The Coast Guard announced it has convened a formal Marine Board of Investigation into the July 19 accident involving a Ride the Ducks of Branson duck boat. The vessel sank at Table Rock Lake near Branson during a storm.

A news release announcing the investigation included a link to the certificate of inspection issued by the Coast Guard on Feb. 7, 2017. The document shows the boat passed inspection but also establishes rules and limitations for the vessel, known as Stretch Duck 7.

The certificate of inspection states the boat "shall not be operated waterborne" when winds exceed 35 mph and/or wave heights exceed 2 feet.

Video and audio from the boat, recovered by divers, showed the lake was calm when the boat entered the lake. But weather suddenly turned violent and within minutes the boat sank.

The National Transportation Safety Board has said the wind speed at the time of the accident was more than 70 mph, just short of hurricane force. Weather forecasts had warned of an impending storm with winds possibly exceeding 60 mph.

The wave height wasn't known, but cellphone video shot by passengers on a nearby excursion boat showed waves that appeared to be far greater than 2 feet tall.

An email message seeking comment from Ripley Entertainment, the company that owns Ride the Ducks of Branson, was not immediately returned.

The Coast Guard said the Marine Board of Investigation is its highest level of investigation. The inquiry will be conducted by a five-member board. No timetable for the investigation was released.

"The Coast Guard will conduct a thorough and detailed investigation to identify all potential causal factors associated with this tragedy," Capt. Wayne Arguin, chairman of the Marine Board of Investigation, said in the news release.

In addition to the weather, the investigation will look at regulatory compliance of the boat and crew member duties and qualifications, the Coast Guard said. The board also will examine whether misconduct, inattention, negligence or willful violation of the law were factors, as well as whether the Coast Guard itself and other governmental agencies offered adequate oversight.

The NTSB and the Coast Guard will work together on the investigation, the Coast Guard said.

Duck boats were designed for military use in World War II. Branson is among several places around the country where the amphibious vehicles offer excursions. Forty-two deaths have been associated with duck boat accidents since 1999.

Nine of the victims in the Missouri accident belonged to one Indiana family. Others killed came from Missouri, Arkansas and Illinois. The dead included five children. Fourteen people survived.