You can camp on the public portion, the boundary as defined here, of the river.
Q: What is considered a public stream?
A: In Texas a stream is public if it is “navigable in fact,“or” navigable by statute.” There is no precise test for whether a stream is navigable in fact. The term is based on the idea of public utility. One court has observed that "[w]aters, which in their natural state are useful to the public for a considerable portion of the year are navigable."1
A stream is navigable by statute if it retains an average width of 30 feet from the mouth up.2 It is important to understand that the entire stream bed is to be included in the width, not just the area covered by water on a given day. A navigable stream may be dry part of the year, but does not lose its character as a navigable stream.
To complicate matters, some Texas land titles originated with Spanish or Mexican land grants, and the law of Spain and Mexico did not distinguish public and private streams on the basis of navigability. Streams were valued primarily as a source of water for household use and for irrigation, rather than a way to move people and goods. So when the sovereign granted land, perennial streams were retained for public use, regardless of navigability, so as to make as much land as possible capable of settlement.3 A stream is perennial if it flows most or all of the year. In determining the rights of holders of title under Mexican grants, the laws of Mexico in effect when the grants were made control.4 So in counties that contain Spanish or Mexican land grants, there are an unknown number of perennial streams which are public streams, even though they may not be navigable.
Q: How do I determine the boundary of a streambed?
A: The Texas Supreme Court has stated that the bed of a stream is “that portion of its soil which is alternately covered and left bare as there may be an increase or diminution in the supply of water, and which is adequate to contain it at its average and mean stage during an entire year, without reference to the extra freshets of the winter or spring or the extreme drouths of the summer or autumn.5” Not clear? Again, the Texas Supreme Court: The streambed is that land between the “gradient boundary” on each bank. The gradient boundary is defined as “a gradient of the flowing water in the stream, and is located midway between the lower level of the flowing water that just reaches the cut bank and the higher level of it that just does not overtop the cut bank.6” Clear as mud? Blame it on those civil judges.
Q: What if the stream is dry?
A: A navigable stream does not lose its public character during periods of low water. A stream is navigable if the bed of the stream averages 30 feet wide from the mouth up, regardless of the actual water level on a given day.