Fish Passage Impediment Classification and Prioritization

In general, fish passage impediments are classified as either natural impediments (e.g. natural waterfalls, extremely high gradient stream reaches), small scale impediments (e.g. log and/or debris jams, landowner-constructed stream crossings, reaches of invasive vegetation), or large scale impediments (e.g. low flow dams, improperly placed or sized road and stream crossing culverts or bridges, snowmobile trail crossings, improperly placed stone ford crossings, berms, dikes, levees). The Program typically does not suggest any changes to allow fish migration around natural fish passage impediments. Small scale impediments are those that can generally be removed or remediated largely with hand labor and hand tools. In general, large scale impediment removals or remediation are addressed with heavy equipment due to the scope and scale of the projects. In general, impediment removal or remediation projects are prioritized based on a number of factors including a Department-developed Stream Reach Prioritization Methodology, landowner cooperation, site conditions and accessibility, cost, available funding, etc.  Connectivity between the AOC and Lake Michigan and identified potential northern pike spawning habitats, as well as potential restorable wetland habitat qualities, is also considered. Impediment removal prioritization also considers the lateral hydrologic connectivity (i.e., the level of channel entrenchment and duration and magnitude of surface hydrology connection between floodplains and channels) of habitat areas to their respective stream channels, the existing quality or restorative potential of riparian wetlands and other suitable northern pike spawning habitats, and the documented occurrences of fish and wildlife species indicative of desirable habitat qualities. In general, full removal of an impediment and restoration of the stream and riparian areas is preferred.

Inventories

Habitat needs to be accessible for all critical life stages to be ecologically valuable to a sustainable fishery. For example, a fish spawning area may be accessible to adults during typical high-water spring flows and provide ideal habitat for juvenile fish to develop, but may become isolated during low water periods preventing young-of-the year to migrate downstream during a critical period. Therefore, ingress and egress to critical habitat are equally important. Various fish species have very different behaviors and physical abilities pass obstacles. Northern pike (Esox lucius) is a native potamodromous fish that inhabits nearshore waters of Lake Michigan, the Milwaukee River estuary, and is also a year-round resident of the river itself. These fish commonly enter very small, oftentimes intermittent, streams to access wetlands and seasonally flooded areas where they spawn. Even though this fish can swim very fast, it can do so only for short distances. In fact, northern pike are one of the weakest swimming native fish in passing long stretches of higher velocity water. In addition, it will not leap to pass cascading water features. For these reasons, northern pike are used as a surrogate to evaluate impediments for all species, and northern pike swimming abilities are considered in all fish passage removal or remediation designs.

The Ozaukee County Planning and Parks Department routinely conducts aquatic habitat and fish passage impediment inventories, which are completed both remotely (e.g. orthophoto analysis) and “on the ground” in the field. In general, potential northern pike spawning areas are identified by qualitative assessments of: 1. Lateral channel connectivity to riparian areas (e.g. floodplain and wetlands) during regular high flows (i.e., channel entrenchment); 2. Herbaceous hydrophytic vegetation density in the channel, on banks or floodplain, or in a littoral area; and 3. Regular riparian flooding (e.g., evidenced by watermarks on trees, drainage patterns, etc.).