A nonnative haplotype of Phragmites australis (Cav.) Trin. ex Steudel has recently expanded its range to become a dominant invasive species in many areas of North America and has thereby become a conservation concern. It is highly aggressive and outcompetes surrounding vegetation by resource competition. Also, by successfully modifying the habitat, P. australis can displace native plant communities and negatively affect other organisms. Phragmites australis abundance has increased significantly at Long Point, Ontario, Canada, a highly sensitive area where 6 freshwater turtle species nest. At these high latitudes, turtles rely upon open, unshaded areas to provide adequate solar heat for nesting and select nest sites based on specific physical characteristics at the time of oviposition. The rapid expansion of P. australis has reduced suitable nesting habitat for many turtle species because the plants' growth during a season alters the microenvironment of turtle nests during incubation, particularly affecting nest temperature, the most important factor for embryo development. Phragmites australis is highly exploitative, and its uncontrolled invasion threatens the reproductive success of freshwater turtle species at Long Point and much of North America.