(CNN) -- A tug boat lookout was on a cellphone call to his mother's house when the barge it was ferrying collided with an anchored tour boat in the Delaware River last summer, according to a report released Monday by the National Transportation Safety Board.

Two tourists died and 26 other passengers were injured in the July 7 collision between the barge and the tour boat near Philadelphia.

The safety board report is a factual finding in an ongoing investigation and does not offer a conclusion as to what caused the accident.

The accident occurred shortly after the tour boat, the DUKW 34, had dropped anchor to deal with a mechanical problem that caused smoked to pour out of the engine. Around 2:37 p.m., a barge propelled by the tug boat, the Caribbean Sea, collided with the tour boat, causing it to sink in 55 feet of water.

According to the report, the Caribbean Sea's master was off duty and below deck. The mate was on navigation watch. The report states that, according to telephone records, the mate made a call to his mother's house at 2:32 p.m. The call, according to the report, lasted until 2:38, one minute after the accident occurred.

The report also states that that between noon and the accident, when the mate was on navigation watch, he made 13 phone calls and answered six.

In radio recordings released by the U.S. Coast Guard last year, an unidentified voice is heard yelling early in the incident, "Hey ferry, ferry, ferry! Whoa, whoa, whoa, whoa, whoa!"

DUKW 34 crew members told investigators that they made radio calls to the tug boat Caribbean Sea that were not answered prior to the collision, the National Transportation Safety Board has said.