Urban lakes provide a range of ecosystem services to their communities but there is little information about the long term biogeochemical behavior of these systems. We have been investigating basic water chemistry and dissolved organic carbon dynamics in Tempe Town Lake, Tempe AZ since Jan 2005. This man-made lake provides both recreational and flood-control services. High-resolution time-series measurements of water chemistry, nutrients, DOC content and DOC composition from Jan. 2005 through the present reveal patterns at a range of temporal scales reflecting water management practices, interannual and seasonal effects due to local rainfall patterns, as well impacts from individual storm events.Over this five year period, the lake has experienced two high-flow events (Jan 05 and Feb 08) that “reset” the lake with fresh water from the Verde and Salt Rivers. In between these two events the lake experienced little input of water, except for rainfall events and the regular inputs from recharge wells. There have also been four monsoon periods during the study period; two years with relatively wet summers (2006, 2008) and two years with relatively dry summers ( 2005, 2007). The bulk DOC concentrations in the lake are generally highest (>6 mg C L^-1) during the winter high-flow events and can exhibit peak concentrations following summer monsoon storms. During dry periods the major ion chemistry in the lake reflects concentration increases due to evaporation; in contrast, DOC concentrations for the same periods decreases due to biological consumption and/or photochemical oxidation. Results from ESI-MS analysis suggest these periods each reflect different DOC compositions and thus sources.