River hazards: current, strainers and low-head dams
Strainers
Downed trees and debris let water pass but trap people and boats. Stay well away and never paddle toward one (PA Fish and Boat Commission).
Low-head dams
Water pouring over a low dam forms a recirculating current at the base that can hold a person, even in a life jacket. They're hard to spot from upstream. Portage around them, and rescuers should throw a line from shore rather than approach by boat (Ohio DNR; Indiana DNR; Iowa DNR).
High water
When flow is well above normal, current is faster and there's more debris. Compare today's flow with typical for the date on our river pages (USGS WaterWatch).
Educational summary of the cited sources, not a safety guarantee. Check local conditions and wear a life jacket.