The role abiotic factors play in structuring ecological communities is one of the most fundamental questions in ecology. At large temporal and spatial scales, heterogeneity of abiotic conditions affects patterns of species abundance and distribution. At smaller scales, these conditions determine patterns of species movement and habitat use. The structuring effect of abiotic conditions may be particularly important along transition zones or ecotones. In the Everglades ecosystem, mangrove-lined creeks link freshwater marshes to estuarine habitats. Previous studies show that these rivers are used by a diverse array of saltwater and estuarine fishes. These rivers may also represent critical habitat for freshwater fishes (including non-indigenous taxa) during seasonal dry-down periods. Historically, these channels and pools served to concentrate fishes for avian predators making this region the most important area in Florida for wading bird feeding and nesting. This study examines temporal and spatial dynamics in the fish community of the oligohaline to mesohaline reaches of ecotonal creeks along the southwest region of Everglades National Park. In particular, we ask: (a) how does use of these river habitats by fishes change over long and short time scales?, (b) how do these changes relate to variation in abiotic conditions (i.e., salinity and freshwater inflow)?, and (c) how do changes in the fish community relate to anthropogenic activity (both previous drainage and impoundment and restoration efforts )? A key objective of this project is establish critical pre-restoration baseline conditions for this habitat. Sampling is conducted in two drainages: Rookery Branch and the North/Roberts rivers. These drainages differ in freshwater inflows and anthropogenic impact. Rookery Branch drains longer hydroperiod marshes and may be affected by restoration to a greater extent than the North/Watson drainage. Sampling is conducted at 15 creeks using electrofishing to target large-bodied fishes and traps to target small-bodied fishes. Sampling is conducted in the wet, transition between wet and dry and dry seasons. The study began in 2004 and will continue through 2010.