How much clean water does carp live in?

pu1. Aquatic animals (water animals) according to water quality are classified into grades 1 to 4 according to the degree of contamination of the water quality by BOD (biological oxygen demand), and are divided into aquatic animals that can live within that range.
Level 1: Very clear water for drinking (Buddlefish, willow dog, bank broker, hardwood fish, Planaria, crayfish, side shrimp)
Level 2: Bathable with relatively clear water (pyramids, hooks, shrieks, sweetfish, stone meat, nematodes, river-birds, oriental day-to-day birds, flying birds, creeps, water lice, and caldaguas (white)
Grade 3: tanned takhaks (fish, carp, loach, catfish, leeches, isomers, dragonflies)
Level 4: The water is black and fish are not allowed to live in contaminated water. (Earthworms, cadavers (red), moth flies, flowers, etc.)
I looked it up and it looks like this
From what I see, carp live in third-class water, so it's not that clean

2017-12-21

OK