The current surface water temperature in Lake Travis is 74 where the average temperature around this time is between 68-70. The thermocline is around 30’ and I would not recommend staying below the thermocline for any period of time with a 3mm. The Comal River is 72 degrees year round. I dive in Travis May through October with only a 3mm. I plan on diving this weekend so I will comment again about my experience on Monday.