The biggest threat from fresh water lakes or rivers is the possibility of bringing in a parasite, bacteria, or nuisance algae, or even varmints you might not want in your tank.
I used to use wood from lake Michigan, and would give it a soak in bleach water a while before use.

The white spots are zebra mussels that were embedded in the piece above.
For fresh cut wood, (as opposed to bleaching) I would soak it in a rain barrel over the winter, yes.. I know, seems like a mighty long time,

These days, near the ocean, I don't worry so much about parasites from salt water.
If it sinks I drop it in the tank.

If it doesn't immediately sink, but looks OK, I let it float, or half float until it eventually does sink, cichlids like to hang under floaters.

There are those pieces that never sink, and are great for terrestrial plant footings like Pothos

Tannins the wood gives off can be a little disconcerting when temporarily staining the tank water, but they are a natural seasonal phenom here, and provide a little antibacterial assist. And if soaked long enough aren't as bad, as my latest addition below.

My favorite log was the one below, but I can't afford a tank that it fits in.
