Pak Sha Tau, the southernmost part of Plover Cove Reservoir in Tai Po, was a small island until the 1960s, when construction work of the world’s first ‘reservoir in the ocean’ commenced.  It was cut off from the sea by the 2.1-metre main dam, which connects the island to Tai Mei Tuk, and the auxiliary dam, which connects to Tung Tau Chau, making it a freshwater lake, as well as a reservoir spreading over the largest area and having the second-largest capacity in Hong Kong.  On one side of the main dam, which stretches into the distance, are placid waters of the lake and mountains; on the other side are waves and sprays dashing on the rock face.  The sweeping sky views overhead make you feel as if you were standing between the sky and the ground.  Tolo Channel comes into view at the auxiliary dam at the east of Pak Sha Tau.  Devonian sedimentary rock, the oldest stratum discovered in Hong Kong, stretches from Wong Chuk Kok Tsui to Pak Sha Tau.  It is estimated that this stratum was formed around 400 million years ago.