Southwest of Houston on the Gulf of Mexico, the snorkeling around South Padre Island has some of the best shore-based snorkel spots in Texas. Although the water visibility is usually not great, you may encounter stingrays, eels, wrasse, triggerfish, trumpetfish and some sharks. The most popular spot is the South Padre jetties at Isla Blanca Park that run out into the gulf from the beach. Alternately, there is interesting snorkeling in Laguna Madre Estuary where the Rio Grande meets the gulf, and you may encounter sea turtles amongst the sea grass (watch out for sharks in the murky water). While you may hear about snorkeling at the Iron Reefs, these offshore natural gas rigs are pretty deep and are better for scuba diving.
Overall, South Padre Island is the 1st most popular snorkel dive spot of all 4 snorkeling dives in Texas.