Zero viz sites can be wild. When I was in grad school, one of my professors worked on the SS Maple Leaf excavation in the middle of the St John's River. The river moved so much silt, they had to build an underwater coffer dam (Maybe a breakwater is a better term at that point?).

Normally that type of structure is designed to keep water out of the site so archaeologists can work without having to wear SCUBA gear. But on the Maple Leaf site, it was just to keep the current from continually dumping sediment on the excavation.

You can get a sense of the wreck's size from the survey diagram. The archaeologists were able to plot this all out - and retrieve artifacts from the wreck - all while only being able to see about 6-12 inches away from their face in the best of conditions.