The edge of the pond is called the margin. For most of the year the water is shallow here and the mud is waterlogged. In summer large amounts of water may evaporate from the pond. This makes the water level fall and the margins dry out. The plants that live here have to be able to cope with this change and have long roots which can search for water deeper in the ground.

As you move out into the pond from the margin the water becomes deeper. Water absorbs light so as the water becomes deeper less light passes through it to reach the sides of the pond. Water plants still grow there but they adapt to the lack of light in two ways.

Some plants such as the water lily produce leaves on long stalks. They grow to the surface and float on it. The leaves receive as much sunlight as a plant on land and are unaffected by the lack of light in the water below.

Pond weeds grow in deeper water still but do not have floating leaves. They have leaves in the form of ribbons or feathers which make a large surface area for catching any light that reaches them.

A few plants, such as the duckweed, simply float on the surface of the water. They have a root but it is not attached to the mud. The root is short but acts like a weight in a fishing float and keeps the plant upright so it can catch light from the Sun and make food.

You may sometimes see a pond in which the water is green. This is due to algae. These are living things that are like tiny plants. They are so small that most of them have a body made from one cell and can be only seen by using a microscope. Even though algae are so small they are adapted for floating in water. They may have spines sticking out of their bodies or drops of oil inside them to stop them sinking to the bottom of the pond. Green pond water is simply made by millions of algae floating in it.

Water plants make food in the same way as plants on land. Those plants which are submerged take in carbon dioxide that is dissolved in the pond water. They take in minerals that is dissolved in the pond water too. When plants make food they also make oxygen. If the plant is making a small amount of food it only makes a small amount of oxygen and this dissolves in the water but if the plant is making a large amount of food it also makes a large amount of oxygen and bubbles form on the surfaces of the leaves.