Hey, there's DockRat! Yay!
In seriousness, it's great to have him pointing out some good points. Well, here's some counter argument, but everything have to be balanced by the readers..objectively or foolishly:
Typhoid, Colera, both can be destroyed by high heat (160°F during cooking). Further more, it can also be killed by stomach acid. However, poor handling by open sores/wounds..well, you're screwed.
Heavy metals get accumulated in the dark meat of the fish. By filleting, you'll see where to remove the residual build up of the dark meat long the backbone. 90% of the heavy metals are accumulated in the internal organs, and not muscles, unless the fishes live more than 5 years at a time.
Well, southern fish do swim north, and northern do swim south. However, the tilapia habits are normally set, and tend to feed and stay within the areas where the foods are abundant. This was fully observed at fish farms..So, best to say that the northern stay at the north, and the southern tend to stay south, unless there is a massive food shortage, which is unlikely. By the way, the southern part of the Colorado River stretch is extremely high in mercury. So, fishing at the southern end is not advised if you're against Salton Sea.
Overall, it's each to his/her own. If the water body is dangerous to fish out off, Rec1 designation would have been changed to Rec3 designation, and limit any contact of water body for any activity by U.S. EPA, or CA EPA.