Light is considered to exist in wave lengths ( actually particles ). Long slowly oscillating wave lengths do not penetrate water very well. Short fast waves lengths penetrate much better. Red is considered the slowest of the visible wave lengths and penetrates the least amount of distance. Violet the shortest and best at penetrating water. It retains it’s color at deeper depths. Faster still is Ultra Violet and it penetrates very well.
The amount of UV light available depends on the Sun ‘s intensity due to cloud coverage, it’s angle to the water and the clarity of the water. UV can penetrate much deeper than we would normally fish.

