Cylindrospermopsis raciborskii is an invasive, toxin-producing, filamentous-heterocystous, N2-fixing cyanobacterium that has recently expanded its range to temperate waterways. Because it is tolerant of a range of environmental conditions, brackish systems like Currituck Sound in northeastern NC, may be susceptible to invasion. Two key research questions were addressed: 1) Is C. raciborskii currently present in Currituck Sound? and 2) What conditions would favor its growth and expansion? In 2007, microscopic analysis confirmed that C. raciborskii was present in Currituck Sound. Metagenomic analyses demonstrated that it has the genetic potential to produce the cyanotoxin cylindrospermopsin. In 2008, salinity in Currituck Sound had risen significantly and C. raciborskii was no longer present in Currituck Sound. The ability of C. raciborskii to grow in Currituck Sound water was assessed using a series of nutrient addition bioassay experiments and demonstrated that C. raciborskii can grow in this water and nitrogen additions increase its growth potential.