I believe it's located between South Padre Island and Mexico ...the map below shows the Brazos Pass.

https://www.google.com/maps/place/Brazos+Santiago+Pass,+Texas+78521/@26.0806488,-97.2269224,12z/data=!4m2!3m1!1s0x866faded4335d37d:0x4a4777922d665ec7

Here is an article from Lighthouse Digest

http://www.foghornpublishing.com/Digest/database/uniquelighthouse.cfm?value=766