Why do some lakes look green or brown?

In one line

The rule

The colour of a lake depends on what is mixed or growing in its water, such as living things (like algae), soil, or chemicals.

Let's understand it simply

Imagine you have a glass of clean water. It looks clear, right? Now, if you mix in some mud, the water turns brown. If you add green paint or green powder, it looks green. The same thing happens in lakes. Things that get mixed into the water or grow inside it can change its colour.

How it works

1. Rainwater or rivers bring soil and mud into the lake. This makes the water look brown or muddy.
2. When there are lots of tiny plants called algae (like green moss), they grow and float in the water, making it look green.
3. Sometimes, chemicals from factories or farms mix with the water. These can also change the colour, making it green, brown, or even other colours.
4. Dead leaves or plants falling into the lake can rot and make the water look dark brown.

The story behind it

Scientists have studied lakes for many years to understand why their colours change. They found that the main reasons are living things (like algae) and things that get mixed in (like soil or chemicals). In India, after the monsoon, many lakes turn brown because of all the mud washed in by rain.

Where you see it in real life

• Village ponds after rain → Water looks brown because rain brings mud from the fields.
• Lakes in summer → Sometimes turn green when algae grow fast in the hot sun.
• City lakes near factories → May look brown or even black because of pollution.
• Temple tanks with many fish → Can look green if fish waste helps algae grow.
• Dal Lake in Srinagar → Sometimes has green patches because of algae.

Why it matters

• Tells us if the water is clean or dirty. Green or brown water often means pollution or too much algae.
• Affects fish and plants living in the lake. Too many algae can use up oxygen, killing fish.
• Important for people who use lake water for drinking, washing, or farming.
• Helps scientists and the government check if a lake is healthy or needs cleaning.

Common mistakes

• Thinking all green lakes are clean. Green colour often means too much algae, which is not good.
• Believing brown water is always dirty. Sometimes, it is just mud after rain, not pollution.
• Ignoring smell. Colour and smell together tell you more about the water's health.

Remember it

If a lake is green, think algae. If it is brown, think mud or pollution.