Damming and water diversions along the Colorado River over the course of the last century have dramatically altered the downstream delta ecosystem. While it is clear that ecological change has occurred, very few data from the pre-dam era (before 1930) exist. Thanks to the preservability of snail and clam shells and accumulations of these shells in the delta, we can retrospectively establish baseline conditions for the community living in the sediments of the tidal flat. Using data from living, recently dead (10s y.o.), and long-dead (100s-1000s y.o.) snails and clams in the delta, we are establishing a baseline and studying the ecological implications of the extensive water diversions along the Colorado River. To date, this has included documenting the range expansion of a predatory snail into the delta (Smith and Dietl, 2016, Journal of Biogeography), demonstrating that water diversions along the Colorado River have had unexpected consequences for carbon cycling in the delta (Smith et al., 2016, Royal Society Open Science), and showing for the first time that water diversions have altered richness and evenness in the bivalve community (Dietl and Smith, 2017, Ecological Engineering). With these data, my collaborators and I are assessing the impacts of recent environmental flows – released under the US-Mexico agreement Minute 319 in 2014 (learn more here) – on the molluscan community. If the amount of water that reached the delta in 2014 was enough to affect the snail and clam community it may return to pre-dam conditions (figure at left, from Dietl and Smith, 2017, Ecological Engineering).