23. Jacksonville, FL

The St. Johns River powers this port city’s economy and some consider it the city’s crown jewel. However, the conservation group American Rivers has named the waterway, which passes through Jacksonville, the sixth most endangered river in the country. High phosphate and nitrogen levels have caused algal blooms in the past. Traffic in and out of Jacksonville’s busy port, which welcomes cargo and cruise ships as well as ferries, has also caused environmental damage. The city is committed to cleaning up the river, and to that end, has adopted laws mandating restrictions on fertilizer use (a major source of nitrates) and limiting irrigation (which helps reduce urban runoff). The next move for Jacksonville is to channel the same river-cleaning energy into other sustainability areas, like increasing public transit and diverting waste from landfills.

(Photo by John Zander)