1.   Dense mats of water hyacinths infest hundreds of ponds, lakes and streams throughout the south from Texas to the Carolinas, plus California and Hawaii.

2.   It grows in dense mats, clogging boat propellers and preventing sunlight from reaching plants on the lake or river bottom.

3.   Some lichens and bacteria have colonized spaces between protective layers of sandstone, and bacteria have formed dense mats at the bottom of ice-covered lakes.

4.   The weed forms a dense mat, blocking sunlight from organisms below, depleting the low concentrations of oxygen and trapping fishing boats and nets of all sizes.