When engineers were throwing huge, specially-designed reinforced concrete chunks across the mouths of three remote bays in the 1960s, the only witnesses were the occasional prawn-netter on a sampan and bemused Hakka vegetable farmers. Those big blocks, shaped like arthritic hands, knitted together to form the stout base of the three dams behind which Plover Cove reservoir was to form. The dam skipped from Ting Kok Tsui village across to Pak Sha Tau Chau (White Sand) island, then to another island, then another, and then back to land. Behind the artificial barrier today, there are 230 million cubic metres of water. When work started in the mid-60s, it was a time of panic. Would the Red Guards turn off the taps? How could we ensure Hong Kong had sufficient to drink? Well, the taps never ran dry and we still get the bulk of our water from over the Shenzhen River. Some may say Plover Cove (and High Island and the never-used desalting plant which has long been dismantled) are a waste of money. I disagree; they were prudent insurance investments by responsible government planners. Today, those two big bodies of water not only contain drinking water, but are key recreational assets. High Island is somewhat locked away in the remoteness of the Sai Kung Country Park, but Plover Cove is easily open to all. Pedestrians and cyclists go up the road which runs atop the dams. There is a car park near the entrance, and bus and mini-bus routes are handy. The first and main dam is about two kilometres long, a sedate ramble with the fresh water lapping on one side and the blue salt water of Tolo Harbour 30 metres below on the other. At present, the dam is full - happy news for Hong Kong's small band of keen freshwater anglers dangling their baits in the 16 lakes and reservoirs stocked with carp and a species called 'big head' which looks ferocious but feeds only on weeds. So far this year, 3,474 have paid $24 for the six-month fishing permit; the season, which began this month, ends in March. When the dams were built, waterworks engineers pumped out as much as possible of the salt water trapped behind them. Over the years, the rains sent streams pouring into the man-made lakes. There were all sorts of legends about seawater fish being trapped and gradually adapting to the brackish and then fresh water: be there sharks in there? Of course, not. Government scientists did not place plump carp in the water because they were nice fellows who wanted fishermen to have fun. No, the species have monstrous appetites to browse on algae and plants. This is why the dam water is so clear and sparkling clean. The fish have grown to spectacular size. Pedalling along the dam crest last winter, I stopped to watch three anglers. They had carp weighing about four to six kilos, beautiful plump creatures. Eat them? You bet, unlike the vile polluted waters on the seaward side of the dam, these fish come from a pure environment. The artificial lakes also hold goldfish (put in by people who want to free their fish) and tiliapa, snakehead, mud carp and hemicutter; quite a variety. It took about five or six years, I recall, for the Plover Cove dam to fill. When it did so and the run-off spilled over the sluiceways, it was a fantastic sight. Word spread quickly, presumably from a passing boat which saw the first waterfall coming from high up the dam. It took just a few minutes for people to get there. The dam was full to the brim - there had been incredible rains - and the water was flowing as if from a lake, which of course is what Plover Cove is. Swept along were some sleepy fish. They suddenly found themselves flapping about on the concrete slipway where eager people were grabbing them as they flashed past; it was like one of those TV documentaries with bears snapping at salmon. This event sparked interest among poachers. Late at night, people would slide makeshift boat on to the placid water and paddle out with nets. My old chum, Chief Inspector Sandy Chalmers whose quarters were alongside the dam and who was in charge of the Village Penetration Unit, once had to go out on a midnight rescue of three men in a sinking boat with a giant 1.8-metre carp. Meanwhile, I have come to the conclusion that the Plover Cove carp all have IQ ratings about the same as a brain surgeon. Toss a chunk of bread in the water and - glop! - a huge mouth rears up from the depths and it is gone. Put a hook in the same piece of bread and it can float for hours, carefully untouched.