Northbrook Junior High seventh grader Sam Heydt cuts down some sand willow plants, an invasive species that needs to be removed, as part of Ecology Day at Techny Prairie October 18, 2012. | Curtis Lehmkuhl~Sun-Times Media

Northbrook Junior High seventh graders (left to right) Sarah Burnham, Isabel Herbst and Lauren Steiner work together cutting down some sand willow plants, an invasive species that needs to be removed, as part of Ecology Day at Techny Prairie October 18, 2

Northbrook Junior High seventh grader Lauren Steiner cuts down some sand willow plants, an invasive species that needs to be removed, as part of Ecology Day at Techny Prairie October 18, 2012. | Curtis Lehmkuhl~Sun-Times Media

Northbrook Junior High seventh grader Daniel Kim collects a sample of river water to perform tests on during Ecology Day at Techny Prairie October 18, 2012. | Curtis Lehmkuhl~Sun-Times Media

Northbrook Junior High seventh graders match up the colors while performing a phosphorus test on river water during Ecology Day at Techny Prairie October 18, 2012. | Curtis Lehmkuhl~Sun-Times Media

Northbrook Junior High seventh grader Kayla Mitter performs an oxygen test on river water during Ecology Day at Techny Prairie October 18, 2012. | Curtis Lehmkuhl~Sun-Times Media