Wide angle adapters 

When and how should they be used ?

There are at least four good reasons, why an additional wide angle adapter lens should be fitted to the camcorder when filming under water (In the case of SLR cameras the standard 30mm focal length are generally sufficient):

Water is a most effective filter for light. After only 5 m (15 feet) the ray of light passing through water has already noticeably lost some of is red spectrum and after 10m (30 feet) all red has vanished from the scenery. Yellow and green follow shortly as you descend.
In other words, if a camera man wants to film an object 5m infront of him and 5m under water (=10m for that ray of light) the colours of that object will be dull and blue. No matter how colourful that little fish really was....
The solution: use as wide an angle as you can. The colours are only right in front and around you. Give the standard wide angle of the camcorder some extra width with an additional adapter lens.

The border between air and water acts light a natural lens and makes objects appear closer then they are. Actually it eliminates the effect of your factory fitted wide angle by a factor of x0.7 !

Water is rarely a clear medium. Sand, plankton and minerals suspended in the water obscure objects further from the lens and make them appear unsharp on the footage.

A diver rarely stands perfectly still in the water (and please do not touch those corrals. It will kill them and spoil the fun of those who follow, including yourself next season !) It is therefore unlikely, that you will actually get that moving fish perfectly where you want him in the picture. The results of your work will only be the odd fin and lots of background...

Your local photography dealer has a selection of wide angle adapters on stock or is able to order them for you.