Perth Canyon is a submarine canyon located on the edge of the continental shelf off the coast of Perth, Western Australia, approximately 22 km west of Rottnest Island. It was carved by the Swan River, probably before the Tertiary, when this part of the continental shelf was above sea level. It is an average of 1.5 km deep and 15 km across, making it similar in dimension to the Grand Canyon. It occupies an area of 2900 km2 and ranges in depth from 700 to 4000 m. Within a few kilometres its depth drops from 200 m down to 1000 m, and then it continues as a deep gully all the way out to the 4000 m depth, which is about another 30 km farther west. It contains the world's largest plunge pool—a depression in the canyon that is 2 km long, 6 km across, and 300 m deep. The canyon is considered "a perfect spot" for deep sea fishing. The Perth Canyon is a feeding ground for pygmy blue whales, especially at the rims of the abyss. It is also a training ground for the Royal Australian Navy Submarine Service, stationed at a naval base at nearby Garden Island. In June 2006 the waters around the Perth Canyon were the site of an ocean vortex 200 km in diameter and 1000 m deep. It was visible from space, and scientists claimed at the time that it had the potential to affect the local climate and the climate further abroad. The vortex was described by scientists as a marine "death trap", as it sucked in fish larvae.