Gastropod shells display a breathtaking degree of morphological diversity. Even with increased reliance on molecular data for modern taxonomic and conservation research, shells still form the basis of most gastropod taxonomy. However, intraspecific variation in shell morphology is common, and poor understanding of intra- vs interspecific variation complicates taxonomy and conservation of many gastropod groups. Nevertheless, intraspecific conchological variation is often attributed to phenotypic plasticity (i.e., a single genotype giving rise to multiple phenotypes). This is particularly true for freshwater snails. Here, I review the evidence of phenotypic plasticity as a causal mechanism of conchological variation across all freshwater snails. Phenotypic plasticity has been well documented in some Panpulmonata lineages (e.g., Radix and Helisoma), but experimental evidence on causes of intraspecific morphological variation is lacking for the majority of freshwater gastropod lineages. Furthermore, phenotypic plasticity, when present, often has a small affect on shell shape. This should not be taken to mean that phenotypic plasticity is not selectively advantageous, but phenotypic plasticity rarely, if ever, causes the presence or absence of discrete shell features like spikes or shell ribs (i.e., plicae or carinae). Broadly, intraspecific shell shape variation in freshwater snails has been speculated to be caused by phenotypic plasticity more often than experimentally demonstrated. I argue that phenotypic plasticity should not be a null hypothesis to explain shell shape variation in freshwater snails. More common garden experimental studies are needed to understand if, and what, environmental cues influence shell shape.