SPF 30 is not going to do anything to you over there, and the water is so transparent in those lakes that the algae has nowhere to hide, really, and so they are developing their own sunscreen, and this is the red color you see.
SPF30の日焼け止めでも 歯が立ちません 湖水の透明度が非常に高いので 藻は隠れる場所も無く 太陽光を遮る仕組みを 発達させました それがご覧の赤い色の理由です