Industrialization in the 19th and 20th centuries made the Yauza "the biggest gutter for waste in Moscow". In the 2000s the ecology improved, with the closing or conversion of old factories and cleanup efforts by the city government. In 2007 the Yauza waters were reclassified from "dirty" to "polluted" status, but in 2008 the trend reversed and pollution in the Yauza exceeded its 2006 levels. As of 2008, Yauza water passing the Moscow city boundary is rated as "polluted", and reaches a "very dirty" level at its inlet. Untreated surface runoff in the Central Administrative District remains the main source of pollution.