The Galveston beaches are not normally clear blue due to a loop current that picks up the roughly 2 million tons of sediment released by the Mississippi River each day and circulates it this way. That water also mixes with the sediment from Red River to add even more sediment to the water. It's not sewer water, just how the natural cycle works. Sometimes the current reverses and we get the blue water that cycles this way from the Yucatan.
If you notice, east (like upstream in the current cycle) of the Mississippi River on the Florida, Alabama and Mississippi coast is usually clear with white beaches.The southern Texas beaches are white sand and a lot clearer due to the sediment being settled out by the time it get there.
Thus ends the irregularly scheduled science minute
