The owner of the whitewater rafting company involved in the Tuesday drowning of a Sausalito resident said the tragedy didn t occur because of low water, and the cause is still unknown.

Mariati Tani, 41, of Sausalito, drowned Tuesday when the raft she was in got stuck on a rock in the Tuolumne River, but “the water level at the time was the normal water level,” said Bob Ferguson, owner of Columbia-based Zephyr Whitewater Expeditions. Tuolumne County sheriff s Sgt. Jeff Wilson had earlier reported that the raft became stuck because the water level was lower, exposing rocks and causing water to funnel between the rocks.

“We feel horrible about the incident,” said Ferguson, who could not explain why the raft got stuck when Tani and her husband, Christy Letham, 50, also of Sausalito, were riding the rapids with a guide from Zephyr. The two were ejected from the raft and Tani was trapped underneath; despite the efforts of a guide to free her, she drowned before the guide was able to get her out.

There were reports based on statements from Wilson that the couple s son was in the raft, but that was not the case, said Ferguson, who said Letham s sister s son was aboard. The incident occurred at about 12:45 p.m., not 1:30 p.m. as earlier reported by Wilson, Ferguson said.

Ferguson acknowledged that the San Francisco Public Utilities Commission had notified rafting companies in the area, including Zephyr, that a generator had failed around 9 a.m. Tuesday and there would be a shorter period in which the normal water levels would be available. The water level was normal at the time of the accident, Ferguson said.

“The water level at the time was the normal water level, but it was a shorter window of time. Normally it s a four-hour release window of high water. They (the commission) let us know that instead of four hours it would be two and a quarter to two and a half hours of high flow,” Ferguson said.

The guide did not vary the route because of the shorter time window, Ferguson said.

“We don t know what happened,” Ferguson said of the accident. “There is only one way to run this rapid and that s the way it was run.” Ferguson said he was out of town at the time of the incident.