Tex. Water Code § 56.144
A district created pursuant to this chapter, special law or other general law may enter into an interlocal agreement with another political subdivision to accomplish the purposes set forth in Article III, Sections 52(b)(1), (2), and (3), of the Texas Constitution. In the event the jurisdictional boundaries of two or more districts or political subdivisions contain all or part of the same watershed of a waterway and one or more of the other districts or political subdivisions determines that the construction of improvements in the watershed would be a public benefit and accomplish the purposes set forth in Article III, Sections 52(b)(1), (2), and (3), of the Texas Constitution, the district or political subdivision shall propose an interlocal agreement to the governing bodies of the other districts or political subdivisions sharing jurisdiction within the watershed. If an interlocal agreement is not executed within 120 days from the date it is submitted to all of the districts and political subdivisions sharing jurisdiction within the watershed, the district or political subdivision proposing the improvements may petition the commission for approval of the proposed improvements. The commission shall conduct a hearing on the proposed improvements and upon a finding that the improvements would be a public benefit, shall approve the plan for the improvements, and the district or political subdivision proposing the improvements shall be authorized to implement the plan within the boundaries of the other district or political subdivision.
Tex. Water Code § 56.144