Why are there bubbles in the water?

There are bubbles in the water. Reason:

When the rain in the sky fell into the water, it took away the air.

The tumbling stirred the water and the air melted in.

Aquatic plants at the bottom of the water carry out photosynthesis and release oxygen.

Sometimes the big "gas" includes animals that die at the bottom of the water, CO2 produced by bacterial decomposition, ammonia and so on.

If the above answers do not solve the problem, please refer to:

Everything has a gap, and where there is a gap, other things can penetrate.

When water comes into contact with air, the air will penetrate into the water, and with the increase of depth, the pressure on the bubbles will be greater and greater.

The bubbles you see will get smaller and smaller.