Question: If the fixed wing lost power over water such as the Hudson River, is it appropriate to lower the landing gears? I would think if a water ditch would be necessary, you would go without wheels down.
Correct. You want to ditch with landing gear UP. If they are down, you run the risk of ripping them off, which increases the chance of sinking faster. Also gear down increases the chance of flipping and cartwheeling.
Also, if there are swells (waves) you want to land parallel to the waves (along the crest or trough) to avoid "hitting" a wave front.
A controlled ditching has a fairly high survival rate, and would be better than taking your chances of landing on a road in that area.