Instream Flows

When rivers and streams are robbed of their life-giving water, water temperatures soar or the streams simply disappear altogether.

This is usually the result of:

Water Diversion
Distribution of water in California is a challenging issue; most precipitation falls in the northern half of the state (in mountain and coastal areas) and most people live in the southern half of the state (in deserts and dry valleys).

Additionally, most of the precipitation occurs in the winter and spring, while most of the use is in the summer and fall. To solve these issues, the state has built dams, diversions and aqueducts to store and move water.

Unfortunately, dams and diversions impact fish in many negative ways including:

Agriculture
Water is often diverted and stream channels are altered in order to supply water for agricultural needs throughout the state.

Blocking migrations
Dams obstruct the natural up and downstream movements of fish.

Dewatering streams and lakes
Dams catch runoff and send it via aqueducts to other locations. Leaving less water for fish.

Changing temperatures and flows
Below dams, rivers suffer from altered temperatures and flow regimes. These changes can result in a major change in fish fauna and habitat.

Entrainment
Fish are carried away or entrained in the diverted water. Often, they end up in a place where chances of survival are low.

Creation of reservoirs
Native fish fauna have a hard time surviving in reservoirs. Generally, these pools of water favor lake-adapted alien species over native stream-adapted fish.

Altering upstream areas
Streams located above a dam cannot recolonize (from other nearby systems) if they lose native fish fauna due to natural or man-made disaster.

Altering estuaries
Dams alter the flow of fresh water into the ocean. Estuaries require large amounts of fresh water to function. They are incredibly valuable watersheds as they are a type of nursery for juvenile salmonids and other fish. They offer an abundance of food organisms so fish can grow quickly before going to sea. If we alter the flow of fresh water, these estuaries suffer.

Groundwater Management
Groundwater and surface water are interconnected. Despite this scientific fact, California’s antiquated groundwater law leaves groundwater use unregulated.

Without a statewide policy for monitoring groundwater use, groundwater pumping for industrial, municipal and agricultural needs leads to overdraft and aquifer depletion. As groundwater and surface water are connected, pumping near springs or streams reduces the flow of water in the stream.

Global Warming
Climate change is also exacerbating the problem because it will ultimately reduce the amount of cold water habitats that our salmonids require.

Water Distribution
Water is often transported within the state to support population demand. For example, Southern California is dependent on water from the Los Angeles Aqueduct that is fed from the Mammoth Basin.