Ironically, many of the pathogenic viruses and bacteria are not harmful to fish and shellfish, but they can accumulate in the aquatic animals nevertheless. When fish and shellfish contaminated with pathogens are ingested, the bacteria and viruses can be passed on to humans. Alternately, some of the pathogens can be transmitted merely through contact with contaminated water. Monitoring for fecal coliform, restricting fish and shellfish harvesting, and prohibiting swimming in contaminated waters are some of the measures designed for the protection of human health. Waterborne bacteria and viruses found in improperly treated sewage and septic systems have the potential to cause serious human sickness or death.
People can acquire typhoid, dysentery, hepatitis, gastroenteritis, and cholera from such waters.
Other ailments range from respiratory troubles to skin disease. Giardia , another pathogen, has been implicated in numerous similar outbreaks over the past twenty five years. Once in a body of water, these substances can become pollutants and affect the water quality, habitat, and organisms in a variety of ways. Many different materials accumulate on city streets and roadways as a result of human activities and improper disposal of waste. Some of these substances may be present in water in forms with relatively low toxicity but may be transformed through reaction with other chemical constituents of water, or through biological processes, into different forms with different toxicities.