Bellevue lies between Lake Washington to the west and the smaller Lake Sammamish to the east. Much of Bellevue is drained by the Kelsey Creek watershed, whose source is located in the Larsen and Phantom Lake green belt and whose outlet is near where Interstate 90 meets Lake Washington's eastern shore. The city is bisected by Interstate 405 running north–south, and the southern portion is crossed from west to east by Interstate 90. The State Route 520 freeway roughly delineates the upper reaches of Bellevue.