The environmental (or in-stream) flow needs of a stream are defined as the volume and timing of water flow required for effective functioning of the aquatic ecosystem – for fish and other needs.
Methods of determining EFNs have been in use in North America for several decades, but in many areas no information on EFNs is available.
In B.C. the introduction of the Water Sustainability Act in February 2016 created a need to determine EFNs for water bodies potentially affected by proposed surface or groundwater extractions.
In locations where significant demand or competition for water exists, such as the Okanagan, scientists, policy-makers, planners, and regulators are now focussed on developing methods to determine appropriate EFN flow regimes.
These efforts are also being driven by an ever- increasing demand for water, and growing frequency and severity of droughts.