lake in the world. large enough to float these massive ocean vessels. but gatun lake serves another purpose- supplying 80% of the fresh water to the people of panama. and that's why we're at the lake this morning. ariel rodriguez is a biologist from the university of panama. he's taking us on a tour of gatun lake, but this tour isn't of the usual sites. it wasn't long before we found what we were looking for. >> behind me that pump is for water but it's out of the water, that doesn't look normal. >> no, of course it's not normal. >> sadly the pump is just the beginning. rodriguez told us to head out onto to the lake and we'd see what has many in panama worried. our boat is a small one, less than 25 feet. tiny on a lake the size of gatun, and no match for traffic. >> wow that's big. >> it's just after noon in the panama canal and that means it's rush hour we've got a container ship going that way, and this big blue one here that is the biggest size of ship that the panama canal right now can handle. >> this is the glovis clipper, a 58-thousand ton vessel. 50 mega-