Presented are experimental measurements comparing the frequency (i.e. - impulse) response (up to 1GHz) for an underwater optical communications channel as a function of water clarity using collimated or diffuse laser light. The measurement technique used is adapted from a previously reported method used for measuring the channel response of collimated laser beam [1,2]. These measurements establish the bandwidth limitations for non-line-of-sight (NLOS) optical links underwater as a function of their operating environment. Comparisons to direct line-of-sight links using collimated beams are also presented.