What is a hose that vacuums water out of lakes or rivers called?

The hose that vacuums water out of lakes and rivers is called Water Suction or Water Transfer Hose.

Usually available in the following materials:

PVC
EPDM
Rubber

"Rubber" Transfer Water hoses are built to handle more rigourous applications which can be subject to abuse, pressures, or elements. They are heavier in weight than PVC or lighter duty EPDM water hoses, but of course more expensive.