We examine, by means of scaling analysis tools and three-dimensional numerical simulations, the time and spatial scales of transport and mixing processes during the cooling phase of the ice-free period in La Caldera, a small lake located at 3,050 m.a.s.l. in Sierra Nevada (Southern Spain). La Caldera is used here as a prototypical example of small high-mountain lakes. Our results demonstrate that transport and mixing in small high-mountain lakes are shaped by the severe changes exhibited at diurnal time scales by the heat fluxes through the air-water interface, strong winds of episodic nature (storms), and the limited horizontal and vertical length scale of the basin. The thermal structure during the cooling phase of the ice-free period undergoes episodic changes that occur at short-time scales, driven by the strong winds with speeds of 15 m s-1 and higher. During those storms, horizontal and vertical mixing and transport is predominantly driven by wind. During inter-storm periods, the oscillatory nature of the air-water heat exchange at diurnal time scales drives convective circulation, which for a small lake occurs at the basin scale and becomes the dominant mechanism of horizontal transport.