First, the burden of proof is on the one making the allegation, in this case the assertion the poor South Texas viz is due to the Mississippi. All I did was ask for some hard data and people tend to get upset when they are challenged for references and cannot respond with them.
Second, nobody said the muck didn't exist. That you have witnessed it doesn't speak anything as to what caused it. I could speculate that the moon was created by UFOs but the fact that I can see the moon in the sky doesn't validate my speculation.
Third, if the "explanations" are so viable there should be some supporting documentation out there. Where is it? In fact, what little data is out there suggests flow gets no further than Aransas, still a long ways from South Padre.
But if I were to make a wild eyed guess (might as well, everybody else is doing it) I would say it's local runoff from the Rio Grande and other Mexican rivers down to Tampico. Check an atlas sometime and you'll see that there are a dozen or more rivers in this area. Do a search on diving along the eastern Mexican coast and you'll find that Veracruz (far south) has pretty good viz but Tampico starts to have South Texas like viz. Now maybe the Mississippi is reaching deep into Mexico as well but given that the known currents flow south to north my best is the source is Mexican rivers.
