Aquatic plants are those that live on or under the surface of water. Bladderworts and water lettuce are some common examples of aquatic plants. The life of these plants as well as aquatic animals can become endangered if there is an oil spill in a water body. The effects of oil on aquatic plants may vary, depending upon the type of oil and surface area that the oil covers.

Oil is a viscous liquid, with lesser density than water. This means that if oil is added to water, it would be insoluble and will float on its surface, thus forming a layer. This layer may prevent the growth of plants if not removed quickly.

Oil is generally classified into five major groups. Oils like gasoline, which fall under the category of "very light" oils, are dangerous to the growth of aquatic plants living in the upper column of water, as light oils like diesel are capable of causing long term damage. Most crude oils, which fall under the class of medium or heavy oils, are difficult to remove from water. Very heavy oils can even mix or sink with sediments in the water and cause severe damage to the plants living in water.

Oil hampers the growth of plants to a great extent. It cuts off the air supply and sunlight, thus making it impossible for plants to carry out photosynthesis and make food. In the absence of photosynthesis, plants fail to germinate and the growth stops. Plants are not able to transpire and most of them die. Kelp and very few other aquatic plants are able to grow again once water is made free of oil.

If oil spills into a water body, even in a small quantity, it very quickly spreads out to a large area. It covers a large surface area and blocks out the air and sunlight completely. This retards all growth activities of the aquatic plants living below the surface. Oil spill on land can also easily reach the nearest water body like ponds, rivers and lakes.

Oil does not only impede the growth of plants, it creates further damage by leading to algae formation. Sometimes, oil in water results into increase in algae which grows very quickly. The widespread algae population in water creates adverse conditions for the growth of other aquatic plants. Also, chemicals which are used to treat the oil cause further obstruction in the growth of plants. Hence, care must be taken while doing a clean-up and harmful chemicals must be avoided.