The loss of aquatic connectivity due to barriers (e.g., dams, culverts) in stream systems is a widespread problem that can have serious implications for fish populations. We have developed the Dendritic Connectivity Index (DCI) as a tool for quantifying loss of connectivity in stream networks, and for prioritizing barrier removal and mitigation. We are in the process of completing the first field test of the DCI using data from two Canadian national parks and assessing the sensitivity of the DCI to barrier (road culvert) evaluation methods. We are also developing methods to integrate measures of habitat quality. Recent research will take fish data from systems elsewhere in North America (Ontario and upstate New York) to further test the DCI using fish mark-recapture data for a variety of stream systems.