Our ignorance of the route was complete. We knew that California lay west, and that was the extent of our knowledge. Some of the maps consulted, supposed of course to be correct, showed a lake in the vicinity of where Salt Lake now is; it was represented as a long lake, three or four hundred miles in extent, narrow and with two outlets, both running into the Pacific Ocean, either apparently larger than the Mississippi River.

Here is a map from 1826 that is the kind Bidwell would have seen. It shows two large rivers flowing from Lake Timpanogos unimpeded to the Pacific Ocean. One river is labeled R. Timpanogos and the other Los Mongos River. The R. S. Buenaventura flows from the smaller Salt Lake. Note the total absence of the Sierra Nevada mountains. Keep in mind that there was next to nothing known about this region up until the 1840s.

1826 Map by Henry Schenck Tanner of North America (detail) Library of Congress https://www.loc.gov/resource/g4410.ct003214/

Another version:

An intelligent man with whom I boarded — Elam Brown — possessed a map that showed these rivers to be large, and he advised me to take tools along to make canoes, so that if we found the country so rough that we could not get along with our wagons we could descend one of those rivers to the Pacific. (John Bidwell, Echoes of the Past, p. 111)

Nope. (Shooting the Rapids, 1871 by Frances Anne Hopkins)

Bidwell doesn’t say whether they took along any boat-building tools. They would have had basic tools along with them anyway, but they weren’t going to be building any boats or floating down to the Pacific Ocean.