he studies his country from the galeta marine center, a science outpost that sits on a gorgeous stretch of beach on panama's caribbean coast. >> its almost impossible to explain egypt without the nile. you can't explain panama without the chagres. it's what makes possible this country. >> the chagres is the river that was dammed up 100 years ago to form gatun lake, at the time the largest man-made 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 th