How do you make it look like you're underwater?

Hello, I am making a first person puzzle game for one of my college courses and in our first map, we have some water at the bottom of an area. It is pretty annoying and ugly that once you enter the water there is no visual effect that appears to show that you are underwater. I am not really looking at something complex but would greatly appreciate it if someone could tell me how to do this.

For in water effect post processing is the thing:

You can go more custom with post processing material, since post process is a shader applied to screen you can use material editor to create your own effect:

Generally, an underwater setting can be somewhat recreated by a rather dark lighting with a blue tint and fog in the distance.
Basically the same way Hollywood used to shoot submarine scenes with miniatures before the days of CGI.
Black background, a blueish spotligt and a fog machineā€¦

Im sure ytou can create some post process effect to enhance it furtherā€¦

You also need to create a post processing volume that encloses the entire water area so that when the player steps in the water, that particular post processing effect kicks in.

As said, look at the post processing documentation.

Fog, scene color, depth of field, blur and other depth based tricks will help you make a great underwater post process material!