Ugh. I hate that.
We had a building in a less than wonderful part of town. When going there for meetings and training sessions, we never quite knew what we would find in the parking lot.
Used condoms. Check.
Rubber tubing. Check.
Dirty underwear. Check.
I've seen all of those in various parks around every city I've lived in, and most cities I've visited. The worst part is that these aren't the "bad" parts of town, they're just...I don't know, easy to hide oneself in?
Actually, where I went to college there was a RiverFest every year, complete with symphony pops concert, lots of street vendors, and fireworks. All of downtown was packed full. Except the river was too polluted to swim in the entire time I was there. Invariably someone would be drunk enough to pee into the river and get arrested, and someone else would either fall in or jump in to try and swim and end up arrested and probably ill from it. I made sure to avoid the riverbanks entirely, lest I accidentally fall in from the crowd jostling me.
Now where I live there's a creek known as "Flush Creek" (not its actual name, but quite an accurate description) in a very high-end part of town. They offer glass-bottom boat tours and have waterfalls with spray along the walkway. I will never go near those areas, but some people pay good money to see what's in the creek, and apparently the waterfall spray is popular during the summer. Ew. Just...ew.