Intraspecific variation in turtle life-history traits has been well documented for many turtle species; however, comparative studies of such traits for the Western Pond Turtle (Actinemys marmorata) are lacking. Here we compare three years of morphometric data on A. marmorata from three study sites in northern California. Our study sites represent various habitat types where A. marmorata can be found and include foothill creeks (BCCR), valley sloughs (SR), and human-made canals (HS). We used maximum carapace length (MCL) as a measure of overall body size and found that A. marmorata differed in body size among sites. For all sites combined, males were significantly larger in mean MCL than females. Among the three sites, both mean male and female body sizes were significantly different (HS > SR > BCCR). Within sites, males were larger than females at SR and HS, but no difference was found between males and females at BCCR. Controlling for body size (MCL), A. marmorata in the foothill creek habitat were flatter and narrower than those in both the valley slough and human-made canal habitats. The observed variation in body size among sites could possibly be caused by differences in prey availability, water temperature, or microhabitat characteristics. Although we have no hard evidence to explain our observed size differences in A. marmorata, we suggest that phenotypic plasticity is responsible for determining maximum size at maturity. Additionally, it is unclear at this time whether fusiform, or compressed shell shape, in A. marmorata offers any adaptive significance in lotic environments.