Waterfalls generally limit water transport to the lower reaches of each river. Some of the waterfalls are spectacular; for example, Kaieteur Falls on the Potaro River drops 251 metres, more than four times the height of Niagara Falls. Other enormous waterfalls are King Edward VIII Falls (256 m), Kumerau Falls (190 m), Oshi Falls (160 – 210 m). In the country are known to exist more than 200 rapids and more than 70 large waterfalls. Many waterfalls are little known and most are not measured yet, it is possible that there are waterfalls in excess of 300 m tall.