They dropped the weight through a hole and saw how deep the rope went. Turns out that the lake was more than 20 feet deep at that point!

The base of the island is made from the roots of the totora reed. Bunches of totora roots are bundled together and they are anchored to the bottom of the lake to keep the island in place. Next, the reed itself is spread out in layers over the base to create the foundation on which life takes place on the island. You can actually feel the island move when a passing motorized boat creates waves. It takes a little getting used to. Our particular island was more than 20 feet above the bottom of the lake. These islands last only a few decades.