The Science Behind the Regional Plan

Download the Environmental Threshold Carrying Capacities

In 1982, TRPA adopted nine environmental threshold carrying capacities (thresholds), which set environmental standards for the Lake Tahoe basin and indirectly define the capacity of the Region to accommodate additional land development. Many of the environmental thresholds will take generations to achieve and a sustained commitment to conservation is imperative. The Environmental Improvement Program is intended to accelerate threshold attainment.

There are nine threshold areas:

Water Quality: Return the lake to 1960s water clarity and algal levels by reducing nutrient and sediment in surface runoff and groundwater.

Air Quality: Achieve strictest of federal, state, or regional standards for carbon monoxide, ozone, and particulates; increase visibility; reduce U.S. 50 traffic; and reduce vehicle miles traveled.

Scenic Resources: Maintain or improve 1982 roadway and shoreline scenic travel route ratings, maintain or improve views of individual scenic resources, and maintain or improve quality of views from public outdoor recreation areas.

Soil Conservation: Preserve natural stream environment zones (SEZ), restore 25% of disturbed urban SEZ areas (1,100 acres), and reduce total land coverage.

Fisheries: Maintain 180 miles of good to excellent stream habitat, achieve nearly 6,000 acres of excellent lake habitat, and attempt to reintroduce Lahontan Cutthroat Trout.

Vegetation: Increase plant diversity in forests, preserve uncommon plant communities including deepwater plants, enhance late seral forests and reduce forest fuels, and maintain minimum sustainable populations of sensitive plants including Tahoe Yellow Cress.

Wildlife: Provide habitat for special interest species, prevent degradation of habitats of special significance.

Noise: Minimize noise disturbance from single events, and minimize background noise disturbances in accordance with land use patterns.

Recreation: Preserve and enhance high quality recreational experience. Preserve undeveloped shorezone and other natural areas, and maintain a fair share of recreational capacity for the general public.

A Threshold Evaluation Report is completed every four years as part of the Agency’s adaptive management cycle–Plan, Check, Do. The report is a comprehensive monitoring program for nine threshold categories, but there are well over 100 indicators measured. The results are compiled and evaluated every four years to see how the Regional Plan is working and to advise the TRPA Governing Board on making critical adjustments in the Code of Ordinances and other planning documents.

View the Threshold Evaluation report