There are some tropical fast-growing trees that are denser than water. In Costa Rica, there are rivers with logs on the bottom as a result of poorly-planned lo

There are some tropical fast-growing trees that are denser than water. In Costa Rica, there are rivers with logs on the bottom as a result of poorly-planned logging expeditions. The trees are so heavy partially because they take up silica from the soil - which is why they're also difficult to cut down.