If the lake is smaller or sheltered then the waves don't have enough space to build up too high. 25-30 kts is very managable, assuming you don't have too large a gust factor. If you are in a large, open body of water then even 15 kts can cause some very large waves.

CAP3000's can handle larger waves, but if you have a strong wind (20kts +) and big waves then you might be able to land, but the problem is that you don't dare turn the plane broadside into the waves/ wind. You can sail backward, but if you are heavily loaded then I would recommend doing it with power on. It helps to keep the plane straight and prevents the heels from digging in backwards and flipping the plane. However, if the wind and waves are so bad that you have to employ this technique then you probably shouldn't be flying.

The amount of wind obviously depends on the brand and size of floats, the landing, the taxi route, or takeoff area, and the load being carried but as a general rule we use 25 - 30 knots for the 180 185 series. If you read the accident reports alot of planes end up upside down when operating in the 35 knots plus range. Most common are digging a wing when landing, turning or taxiing down wind. Landing or taking of in narrow rivers while close to high treed shorelines in heavy cross winds can require very aggressive co-ordinated control inputs just to maintain control of the aircraft.
Carefully thinking ahead before the flight and planning your taxi and takeoff run and then doing the same with your landing location and taxi path will help you decide how much wind is acceptable. Pays to allow for a little more wind than forecasted at the other end. The pendulum effect of turning in high winds and big waves in open water is especially dangerous as it exposes the underside of the wing to the wind. No two situations are ever exactly the same so careful preflight planning, caution and working your way up to higher winds over time is the safest. Seems every experienced float pilot can recount play by play some wind situation that is still pretty vivid in their mind.