Many of the ecosystems in the Blanco River Basin have remained relatively intact and minimally impacted. However, fish assemblages (PDF) are an exception to this trend and have experienced significant negative impact by human driven changes.
In the past, the decline of southern native fish populations have been primarily due to habitat degradation (Warren et al 2000). Impacts from stormwater run-off, urban contamination loads, and erosion increase sediment and nutrient loads.
Range restriction of these species from dam construction have altered hydrologic regimes resulting in the following:
- Declining fish numbers
- Reduced connectivity between upstream and downstream river stretches affecting reproduction and feeding (Porto et al1999)
- Restricted movement of fishes resulting in reduced upstream biodiversity
- Decreased periodic discharge of floods in lower river segments important in cyclical ecological disturbances
- Create opportunities for dominance of species associated with lake (lentic) systems