Answer:
fastest in rivers, slowest in groundwater
Explanation:
Water bodies undergo self purification by conversion of pollutants into harmless substances through various factors such as:
1. Production of Oxygen as a by-product of photosynthesis by aquatic plants. The oxygen helps in the self- purification of the water body.
2. Aquatic bacteria and plants also help in the release of nutrients which helps in self purification by decomposition of matter in the water.
Rivers, lakes and groundwater are the options. However the largest water body in these options is the River and it contains more amounts of oxygen and aquatic plants which makes self purification faster.
The Lakes are second in size to the river.
The Groundwater contain lesser amounts of oxygen and aquatic plants which makes it the slowest in self purification.
