quality for the endangered Southern California Distinct Population Segment of steelhead. According to the article, the snails have expanded "from the first confirmed sample in Medea Creek in Agoura Hills to nearly 30 other stream sites in four years." Researchers at the Santa Monica Bay Restoration Commission believe that the snails' expansion may have been expedited after the mollusks traveled from stream to stream on the gear of contractors and volunteers. In Colorado, Boulder Creek and Dry Creek have infestations of New Zealand mudsnails. The snails have been present in Boulder Creek since 2004 and were discovered in Dry Creek in September 2010. Access to both creeks has been closed to help avoid spread of the snails. In the summer of 2015 an industrial-scale wetland rehabilitation project was undertaken in northeast Boulder to rid the area of a mud snail infestation. Ecology Habitat The snail tolerates siltation, thrives in disturbed watersheds, and benefits from high nutrient flows allowing for filamentous green algae growth. It occurs amongst macrophytes and prefers littoral zones in lakes or slow streams with silt and organic matter substrates, but tolerates high flow environments where it can burrow into the sediment. In the Great Lakes, the snail reaches densities as high as 5,600 per m² and is found at depths of 4–45 m on a silt and sand substrate. This species is euryhaline, establishing populations in fresh and brackish water. The optimal salinity is probably near or below 5 ppt, but Potamopyrgus antipodarum is capable of feeding, growing, and reproducing at salinities of 0–15 ppt and can tolerate 30–35 ppt for short periods of time. It tolerates temperatures of 0–34 °C. Feeding habits Potamopyrgus antipodarum is a nocturnal grazer-scraper, feeding on plant and animal detritus, epiphytic and periphytic algae, sediments and diatoms. Life cycle Potamopyrgus antipodarum is ovoviviparous and parthenogenic. This means that they can reproduce asexually; females "are born with developing embryos in their reproductive system." Native populations in New Zealand consist of diploid sexual and triploid parthenogenically cloned females, as well as sexually functional males (less than 5% of the total population). All introduced populations in North America are clonal, consisting of genetically identical females. As the snails can reproduce both sexually and asexually, the snail has been used as a model organism for studying the costs and benefits of sexual reproduction. Asexual reproduction allows all members of a population to produce offspring and avoids