Two fathers push children in buggies across a waterfall The waters might look low at the moment but you never know what is there - and it is very slippery. A local coastguard team took a picture of the fathers in the water, warning: "This is just reckless and dangerous." A Penarth Coastguard spokesman added: "Being swept over Blackweir is like being dumped by a constant barrage of pumping waves with the churning water forcing you down. It only takes ankle deep water to knock you off your feet and only 60 seconds to drown. Fast flowing water hides dangers such as rocks, holes, debris and fallen trees trapping the swimmer. Sergeant Adrian Snook of South Wales Police warned people to stay out of the river even during the hot weather. Sgnt Snook said: "We cannot emphasis enough just how dangerous this can be." Natural Resources Wales manages the rivers in the Welsh capital and said weirs could be "extremely dangerous." A spokesman added: "Although the waters may appear calm, they can have strong currents making it dangerous to paddle, swim or boat."