Many of the campsites are right on the water, which is the Arroyo Colorado, a canal that runs east-west to the Laguna Madre, the bay between the south Texas shoreline and South Padre Island. I've visited the park many, many times over the years because of its proximity to the Laguna Madre. I fish from a kayak, and have tried fishing South Padre Island, Port Mansfield, and Boca Chica Beach with some success. But I always go back to Adolph Thomae County Park because I have better luck there. I don't have to worry about leaving my vehicle unattended, either.
What else? There is a website - http://www.cameroncountyparks.com/adolph-thomae-park - that has all the info you need if you plan to visit. There are even a few pictures. But if you want to get a much better look at the park, download and load Google Earth and type 'Adolph Thomae County Park' in the search bar. For some reason, the locator map on thedyrt is way off. The latitude for the park is 26°20'42.65"N and the longitude is 97°24'50.43"W. I've tried editing the location to no avail.
If you use Google Earth, you'll see that there are 2 lighted fishing piers that are free to park visitors. There are also 3 public restrooms - one at each of the piers and a third between the two large parking lots at the end of the road. There are also two boat ramps at the end of the park road.
It's 3 miles from the park to the Laguna Madre, so if you're bringing a kayak be prepared to paddle for about 45 minutes before getting to the bay. The park opens at 6:00 AM, and the fishermen with motorboats start lining up about 5:45 AM. If you want a parking spot near the water, get there early. I've found that the best parking lot to use is the next-to-last. The water is just a few steps from the parking lot, and the grade down to the water is not that steep. There are no streetlights in the next-to-last parking lot - at least not yet - , so bring a headlamp. It's a relatively new parking lot, so lights may be installed at some point.