The organs are known as Vestigial organs. The evolution from land-dwelling animal to the marine animals has led whales as well as dolphins, to lose hind limbs. The pelvic and leg bone serves no purpose in them and just provide the anchorage to muscles
Fertilizers are inorganic o organic nutrients highly rich in elements like nitrogen, potassium and phosphorus which are essential for the growth of plants.
The application of excess fertilizers in the soil causes the surface run off as well as leaching of these nutrients into the soil from where it is gradually transferred into the nearby water bodies, in this case the lake adjacent to the farmer's property.
In the lake, these nutrients promotes the growth of plants like algae.
The excessive growth of algae in the lake disturbs he ecological balance of the lake and causes a dearth of oxygen in it. This phenomenon is said to be called Eutrophication.
The reduction in the level of oxygen in the lake causes the animals, like fishes, in it to gradually die.
