@BCM thank you for your words. I have read a lot of literature on mental toughness, and have had to base my study around previous study in other sports due to the lack of literature in water skiing. Some of the particularly interesting studies to me are listed below. All of these I have been able to access through either google scholar or my library database.
Jemmy, S., & Easvaradoss, V. (2018). Mental Toughness and Positivity as Predictors of Performance Strategies Used Among Competing Athletes. International Journal of Sports Sciences & Fitness, 8(2), 98-119.
Chen, M. A., & Cheesman, D. J. (2013). Mental Toughness of Mixed Martial Arts Athletes at Different Levels of Competition. Perceptual & Motor Skills, 116(3), 905-917
Biglari, S., Sanatkaran, A., Bahari, S. M., & Montazeri, M. (2015). The Comparison of Team and Individual Male Athletes, Mental Toughness at Different Levels of Skills. International Journal of Basic Sciences and Applied Research, 4(2), 127-132.
Slimani, M., Miarka, B., Briki, W., & Cheour, F. (2016, June 7). Comparison of Mental Toughness and Power Test Performances in High-Level Kickboxers by Competitive Success. Asian Journal of Sports Medicine, 7(2), e30840.
Chen, M. A., & Cheesman, D. J. (2013). Mental Toughness of Mixed Martial Arts Athletes at Different Levels of Competition. Perceptual & Motor Skills, 116(3), 905-917.