In a water body, too much sewage leads to

When there is too much sewage in a water body, it can lead to an increase in the bacterial population. This is because sewage contains organic matter and nutrients that can provide food for bacteria to grow. However, as the bacteria grow, they use up oxygen from the water. If there is too much bacteria, it can lead to a decrease in the level of oxygen in the water. This is called "eutrophication." A decrease in oxygen levels in water can be harmful for aquatic animals. Many fish and other aquatic creatures need a certain level of oxygen to survive, and if there's not enough, they can become sick or die. This can also have a ripple effect throughout the ecosystem, as the loss of certain species can affect the food chain and balance of the environment.