The Indian River watershed drains an approximate area of 8,055 ac (3,260 ha) and flows through the park into Jamestown Bay from the mountains northeast of the town. The section of the Indian River that runs through the park is approximately 0.64 mi (1 km) long and includes the entire mouth of the river. While the river supports a variety of aquatic habitats including river delta, estuaries, floodplain channels, and coastal intertidal areas, it is also central to biotic resources in the park. The river is a primary freshwater resource in the region: important for wildlife and the growth and propagation of fish, shellfish, and other aquatic life. It is an important source of water for aquaculture and visitor recreation. A number of stakeholders maintain water rights to the Indian River and have a direct interest in preserving the quality of this water resource.
The Indian River watershed is characterized by steep topography, well-drained shallow soils, and high drainage density. It exhibits a rapid response to rainstorms, which often cause rather large daily fluctuations in stream flow. Hydrologic calculations indicate that peak runoff occurs within six hours of a storm center passing over, with nearly all rainfall running off in 12 to 24 hours. River flow ranges from approximately 20 cfs to 6,400 cfs (100-year flood). River discharge generally peaks in September and October and gradually declines throughout winter and early spring. Snowmelt at high elevations results in moderate flow increases in May and June. Minimum flows are most common in December, March, and July.
Monitoring water quality and quantity in the Indian River is critical. Monitoring gives park managers the ability to observe changes in the river’s flow, temperature, salinity, and dissolved oxygen, and call attention to emerging problems.
Water temperatures are important for specific biological processes including fish metabolism, growth rates, and oxygen solubility. Water temperature greatly influences water chemistry and the organisms that live in aquatic systems. Not only can temperature affect the ability of water to hold oxygen, it also affects biological activity and growth within water systems. All aquatic organisms, from fish to insects to zooplankton and phytoplankton, have a preferred or ideal temperature range for existence. As temperature increases or decreases too far past this range, the number of individuals able to survive eventually decreases. In addition, higher temperatures allow some compounds or pollutants to dissolve more easily in water and can be more toxic to aquatic life. Salmonid larvae are particularly sensitive to warm water, so increases in water temperature can be problematic for streams that support salmon populations, such as the Indian River.
Dissolved oxygen (DO) is critical for aquatic organisms. The concentration of DO in a water body is closely related to water temperature; cold water holds more DO than does warm water. Therefore, DO concentrations are subject to seasonal fluctuations as low temperatures in the winter and spring allow water to hold more oxygen, and warmer waters in the summer and fall hold less oxygen. The hydraulic characteristics of the stream, photosynthetic or respiratory activity of stream biota, and the quantity of organic matter present also contribute to high or low levels of dissolved oxygen. Management and monitoring of dissolved oxygen levels is particularly important in the park, because a number of prominent species require highly oxygenated water at every stage in their life cycle, including salmonids and many aquatic insects. Aquatic insects are indicators of the biological health of aquatic ecosystems. Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) are particularly sensitive to changes in their environment and will disappear or be reduced if aquatic conditions deteriorate and other more tolerant organisms will replace them. A high percentage of these taxa indicates an unimpaired stream with good water quality.