A great shot Martin! And I just love the constrast and the bright pop of color with the kayaks! As for cropping the sky, I think actually that you should play with it a bit. Maybe apply the rule of thirds in a different proportion. There is quite a lot of vast blue here and by making the lake with the kayaks the heavy 2/3 you might also highlight the mountains a bit more. On the other hand, you've got the mountains and lake horizon point very central here, so it works well. That's a personal call, and it's your beautiful photo!