A product of microbiological decay of plant and animal protein.
Its presence in raw surface waters usually indicates domestic or agricultural pollution.
Above certain levels it is toxic to fish.
| Method | Range | Steps (ppm) | Approx Number of Tests |
| Test strips | 0-0.6mg/L | 0, 0.25, 0.5, 1, 3, 6 | 25 |
