Fish are generally considered clean and fresh, but several environmental factors can make fish unfit for consumption. The factors relate to the food of the fish itself – the fish is what it eats – and to the cleanliness/safety of the water body. Fish can also be contaminated by poor handling at any stage from being caught to being eaten.

Water bodies can be contaminated by:

• Industrial chemical wastes which may contain heavy metals.
• Farm chemical drainage containing pesticides which may bioaccumulate; for example, DDT accumulates in fish tissues.
• Domestic and commercial wastes, drainage and runoff, which may be contaminated with faeces or other pollutants.