The 30-acre Horno Creek Water Quality Basin and Wetlands at the southern end of Ladera Ranch opened in 2003. It collects 75% to 85% of the urban water run-off and drainage from Ladera Ranch after it has filtered through the Sienna Botanica. An undertaking of enormous scale, Horno Basin is another example of the innovative partnerships Rancho Mission Viejo has established with the County of Orange, the Army Corps of Engineers and the Santa Margarita Water District to protect local watersheds and create or restore wetlands.