The New Zealand mudsnail (NZMS) is an invasive first discovered in Olympia, Washington's, Capitol Lake in 2009 and has since been detected in the lake at high densities. In this study, we review salinity tolerances from NZMS investigations conducted in the wild and in the laboratory. Based on the review, we backflushed Capitol Lake with saltwater introduced through a dam that connects the lake to the sea to examine the effect of increasing the lake's salinity on NZMS survival. We present pre- and postbackflush survival rates from 26 sample stations, 8 of which were supplemented with the topical application of salt. Increasing the lake's salinity decreased survival, and the topical application of salt increased the effect. Sample size and location had a significant effect on survival. We subjected pre- and postbackflush NZMSs to laboratory saltwater trials and used the data to construct a generalized linear model to predict survival rates under various salinity exposure regimes. More NZMSs were killed in response to the backflush than was predicted by the generalized linear model. Water temperatures in the lake were lower than those used in the laboratory and this may have decreased NZMS resistance to increased salinities in the lake.