Continuity mistake: Sacajawea (Donna Reed) dives into the water to retrieve some important maps, which have fallen in and been taken to the back of the boat. When she dives in, the maps are back to the original area they fell into, when they should have been quite a distance from where they landed in the water.
Continuity mistake: Wallis is showing his idea to the doctor and draws on the sketch of the dam. Shortly after, he shows the doctor the same sketch again and the middle line we saw Wallis draw has now changed position. (00:06:40 - 00:07:50)