RedactedNarrative: V1 was fishing in a tournament from 7 am-3 pm with a trolling motor. They came back to the dam location and near the dock when they noticed a lot of water in the boat.  They started the large motor to quickly head back to the dock.  When at the dock, the boat filled with water, rolled over and sank.  Plug was still securely in the boat and unsure what failed.  No alcohol was involved and neither occupants were wearing life jackets.