The Trinity River is world famous for huge alligator gar....the River Monsters TV show showed how its done and also one of the top guides. Folks come from all over the World to fish for them....but seems like some locals are totally unaware of the fantastic fishery.
They are in the river all above, below, and in Lake Livingston. If you look for the river in Houston as advised, you won't find it...but may find some good gar fishing in the bayous there. Check out http://www.texasfishingguides.org/kirkland/
...over 100 IGFA gar records.