A football field is seen on the dried bottom of the Blue Lake near Imotski, Croatia, Sept. 20, 2020. Lying in a deep sinkhole, the water level of the karst lake in southern Croatia varies with seasons. (Ivo Cagalj/Pixsell via Xinhua)

A football field is seen on the dried bottom of the Blue Lake near Imotski, Croatia, Sept. 20, 2020. Lying in a deep sinkhole, the water level of the karst lake in southern Croatia varies with seasons. (Ivo Cagalj/Pixsell via Xinhua)

People play football on the dried bottom of the Blue Lake near Imotski, Croatia, Sept. 20, 2020. Lying in a deep sinkhole, the water level of the karst lake in southern Croatia varies with seasons. (Ivo Cagalj/Pixsell via Xinhua)

People play football on the dried bottom of the Blue Lake near Imotski, Croatia, Sept. 20, 2020. Lying in a deep sinkhole, the water level of the karst lake in southern Croatia varies with seasons. (Ivo Cagalj/Pixsell via Xinhua)