Lake Maracaibo
The environment of the lake has several problems. Part of the lake is infested with the duckweed Lemna. Duckweed are plants that float freely on the water. The problem with Lemna is that it spreads very fast. Its cover of the water can double in 48 hours. The plants can only be removed physically. In mid 2004, about 18% of the lake  was covered with it.