That is a storm drain or called storm sewer in some parts of the country which collects runoff. Very different from a sewer which is usually shit and piss and tampons and used condoms. Not that it makes it any better But if you've ever fished the San Diego River or any other creeks in SD its essentially the same thing because all storm runoff ends there eventually. Lots of fun to fish and i've done it a bunch. But I avoid touching the fish and definitely don't eat them! That's just me though.