The research aims to study the effect of the rehabilitation program using water exercises to improve the functional efficiency of the muscles of the knee joint affected by an anterior cruciate ligament tear. To achieve the objectives of the research and to test its hypotheses, the researcher used the experimental method, as it is the appropriate method for the nature of the research. A model of experimental designs was used, which is the pre- and post-measurement for one experimental group. The research population consists of athletes. The research population consists of athletes with a torn cruciate ligament who are scheduled to undergo surgical intervention during and who are attending motor rehabilitation centers in Minya Governorate for the years 2023/2024. The research sample was chosen intentionally and the basic research sample consisted of (14) injured athletes. With a cruciate ligament tear and surgical intervention was scheduled, the researcher found the effectiveness of a rehabilitation program using water exercises to improve the functional efficiency of the knee joint muscles affected by an anterior cruciate ligament tear. This was demonstrated by the presence of statistically significant differences between the average ranks of the two measurements before and after rehabilitation (before surgical intervention) for the group. The functional efficiency variables for the group under study were in favor of the measurement after rehabilitation and before surgical intervention, and the percentage changes between the two measurements before and after the rehabilitation program (before