I firstly though you mean under water sea on whole image. But after examine your image, I assume you mean water for that pond, correct?
If it is, then usually pond has more clear water so there is no necessary to add blue filter or such. Usually the more closer, you can see bottom like fish swim on top of it, while the further away you will only see reflection of the above. I suggest google pond and see how it works
The water always has bluish tones the further the distance goes from the point of view in front of you. The water "sky" where the suns will be dispersed by the surface waves, making rays as the light penetrates the water. The further objects you would need to add bluish tones of background as they blend more and more into background as the distance goes, and eventually fade into the distance.
Any time I paint underwater scenes, air bubbles floating to the surface always helps the effect. Tiny bits of floating debris. Dirt billowing like smoke. These types of things help sell the effect of a different kind of gravity.
I did this painting a while back, trying to show a deep sea creature backlit by a spot light. I kinda wish a cooled the colors off to give it a murkier feel, but the debris and bubbles help a bit I think.
Under water has light fading in deeper waters. The surface of the water has ripples. The light forms beams and ripples showing weaker and stronger light, because of magnification from the high peaks on the surface.
You can add what you expect to see under the water like coral reefs, fish, sharks, jelly fish, moss, and barnacles. I made something look like it was under water.
I created a 3D shuttle I called Cargo Ship for a spaceship that can go underwater. You can see I painted a rock covered a rock with moss. What makes it look more underwater is the light from the rippled surface. I pained in the light hitting the shuttle to help with the effect.
A long time ago, I painted a sub with turbines to drive it and lighting like a car headlights. Then in the distance I painted one heading towards it. There is a lot more you can do to make it look like underwater like a heard of fish like a flock of birds in the sky.
How far away it is don't effect the lighting, because it comes from the surface of the water. if the water is a little dirty, then it will be hazy by distance. It can look pretty clear, but deep in the water the light fades and can't reach deep water. I am sure it would go deeper at noon, than at sunset, because the angle of the sun will make it fade faster because the light needs to go through more water.
I would add light rays coming on the top of the picture, and not just a blue filter, but a gradient, with the bottom color a very dark blue and the top color a royal blue. Look up references, that will help aswell !