Neither of these is prime habitat for aquatic organisms, and any critters that are still there are often small, making it easier for them to slip through a net. If they do make it onto the net, they're often buried in mud and sand. When SOS and Baltimore County first implemented our biological monitoring program, we found that monitors in highly degraded areas were having trouble seeing and collecting critters from the net. Think early and often about safety Safety is an issue for every monitoring program. However, in city monitoring there are additional considerations.
Monitors are often sampling from road bridges, so there's traffic to watch out for.
Crime can be a real concern in some locations. Feeling unsafe can also be a function of preconceived notions or unfamiliarity. It is not unheard of for monitors from upstream communities to express concerns about monitoring in certain parts of a city that they perceive as having a high crime rate. Whether a place is truly dangerous is not the only issue. If a volunteer feels unsafe about a location, don't try to talk them out of their fears even if you believe the site is safe.