Class I (clean)

Class II (fairly clean)

Class III (general)

Class IV (polluted)

Class V (heavily polluted)

Class V+ (seriously polluted)

Dissolved Oxygen

>8

>6

>4

>3

>1

<1

Permanganate Index

<2

<4

<6

<20

<50

>50

BOD₅

<1

<3

<5

<15

<30

>30

COD

<15

<15

<20

<30

<40

>40

TP river/(lake)

<0.02 (0.01)

<0.1 (0.025)

<0.2 (0.05)

<0.3 (0.1)

0.4 (0.2)

>0.4 (0.2)

TN

<0.2

<0.5

<1.0

<1.5

<2.0

>2.0

${\text{NH}}_4^{+}\text{-N}$

<0.15

<0.5

<1.0

<1.5

<2.0

>2.0

Volatile Phenols

<0.001

<0.005

<0.01

<0.1

<0.5

>0.5

Cyanide

<0.01

<0.05

<0.1

<0.5

<2

>2

Arsenic

<0.01

<0.04

<0.08

<0.3

<1

>1

Mercury

<0.00001

<0.0005

<0.001

<0.01

<0.05

>0.05

Chromium

<0.01

<0.02

<0.05

<0.2

<1.0

>1.0

Cadmium

<0.001

<0.005

<0.01

Lead

<0.01

<0.05

<0.1

Copper

<0.005

<0.01

<0.03

Petroleum

<0.05

<0.3

<0.5

<1.0

<3.0

>3.0