The Superfund program -- under which some of the nation's most contaminated sites are cleaned up -- is taking on some of the most complex projects in its history.

Many advocates welcomed the trend, saying that contaminated urban rivers had simply been writtten off in the past.The New York Times reports that the U.S. Environmental Protection Agency, which administers the program, is taking on more cleanups of urban waterways that have long histories of pollution and are costly.

The Hudson River cleanup is one example of this trend toward ecosystem-wide cleanups, as is the Diamond Alkali Superfund site on the Passaic River in New Jersey, which drains into the New York Harbor. Other large Superfund cleanups are soon to begin in Oregon and Washington state.

The Times reports that while river cleanups are not easy, new technologies and information have made them more feasible.

The Superfund, signed into law in 1980, currently has over 1,300 sites listed as contaminated by hazardous substances, including 87 in New York.