Radio is very poor underwater. Especially deep water. Ultrasonic communication can be used, but probably not suitable for exploring the interior of a shipwreck - probably needs line-of-sight to work properly.
Visible light is pretty much just the portion of the EM spectrum that is poorly absorbed by water [0] (and that is also produced by the sun and also poorly absorbed by atmosphere)
If radio worked well in water (where eyes first evolved), then we would just "see" radio waves (except in practice the Sun doesn't make enough of them that reach Earth).
[0] http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.h...