Use of vhf16 for Texas Intracoastal waterway

Why does the USCG allow nonstop routine Texas Intracoastal Waterway discussion on vhf channel 16? This seems to be used in place of vhf ch13 on the Texas Intracoastal waterway south of Houston.
Did I miss a memo on vhf channel 16 usage?

The CG does not monitor channel 16 for that purpose although they might occasionally step in. The FCC is the agency responsible but they have no enforcement mechanism to prevent abuses. You can always advise those using the channel incorrectly to switch to a working channel. Expect a variety of responses including some physically impossible to comply with.