Indicator
Stream Habitat Condition
2023 Evaluation
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This indicator measures the amount of excellent, good, and marginal habitat in streams of the Tahoe Region. Stream habitat includes features such as gravel, boulders, large wood, pools, riffles, and riparian vegetation that provide habitat for a wide variety of organisms. Streams are critical to the Tahoe Region's water cycle by feeding freshwater to lakes and ponds, recharging groundwater, providing habitat for a wide variety of aquatic and terrestrial organisms, and corridors fish and wildlife migration. Past practices such as gravel mining, logging, and development along stream corridors negatively impacted fish habitat. Regional programs such as removing impassable culverts and stream habitat restoration projects aim to improve stream habitat. The health of Tahoe's streams is assessed by evaluating physical stream habitat (large woody debris, boulders, etc.) and benthic macroinvertebrates (mayflies, stoneflies, etc).

Miles Of Stream Habitat In Excellent Stream Condition.jpg
Status

Average California Stream Condition Index (CSCI) scores of all trend sites within the Tahoe Basin for each time period. Site scores are put into three different categories of excellent (CSCI >0.92), good (CSCI = 0.79-0.92), or marginal (CSCI <0.79). The CSCI measures the biological health of streams by assessing the community of benthic macroinvertebrate in perennial streams.

Data is provided by TRPA. Access detailed datasets on Tahoe Open Data, including: Stream Survey Locations, Basin-wide Annual Average CSCI, Stream Miles Condition Class per Threshold Evaluation Period and Stream Condition Data.

2023 Evaluation
See how thresholds are evaluated
Status
Somewhat Worse Than Target
Trend
Little or No Change
Confidence
High
Applicable Standard
F1-F3: As indicated by the Stream Habitat GIS data, amended May 1997, based upon the re-rated stream scores set forth in Appendix C-1, of the 1996 Evaluation Report, maintain: F1) 75 miles of excellent stream habitat, F2) 105 miles of good stream habitat, F3) 38 miles of marginal stream habitat.
Key Points
  • 4,890 linear feet of stream have been restored by Environmental Improvement Program (EIP) partners since 2020. These EIP projects have allowed the Tahoe Region to meet its goal for SEZ restoration for the first time in 2020, with recent projects such as the Upper Truckee River Marsh project and restoration work on Saxon Creek following the Caldor Fire putting the Region over the top for meeting the goal.
  • The Caldor Fire negatively impacted streams on Lake Tahoe's south shore. Seven sites were sampled before and after the Caldor Fire from within the fire perimeter. Six of those sites had a decreased CSCI score and one had no change.
  • The stream fish habitat threshold standard was met in 2020, but there are still numerous stream segments identified for restoration, and stream restoration contributes to numerous threshold standards.
  • Over the last 40 years many of the stream restoration projects identified in the 1982 Threshold Environmental Assessment have been completed by Environmental Improvement Program (EIP) partners.
  • The use of benthic macroinvertebrates and associated physical/chemical stream measurements (i.e. bioassessment) to assess overall biotic health of streams is a widely accepted practice used by the EPA and all 50 states in their water quality programs.
Evaluation Map
Description

Stream ratings as of 2022 for the Tahoe Basin. Stream ratings incorporate stream health indicators such as fish passage, in-stream habitat, macroinvertebrate diversity, among others. 

About the Threshold
Streams are critical to the Lake Tahoe Region's water cycle by feeding freshwater to lakes and ponds, recharging groundwater, providing habitat for a wide variety of aquatic and terrestrial organisms, and corridors fish and wildlife migration.
Tahoe's streams continued to recover from historic impacts from gravel mining, logging, and development along stream corridors. The Regional Plan and the regulations of partners prevent the additional disturbance of streams, riparian areas, and stream environment zones. Regional programs such as removing impassable culverts and stream habitat restoration projects improve stream habitat.
Delivering and Measuring Success

EIP Action Priorities

EIP Indicators

Example EIP Projects

Monitoring Programs

Rationale Details
Somewhat Worse Than Target. The total length of streams in Tahoe has varied through time as a result of improvements in mapping. To avoid bias as a result of methodological differences in stream delineation, the threshold is assessed relative to the proportion of stream lengths in the threshold standard. The threshold standard establishes a goal of "75 miles of excellent, 105 miles of good, and 38 miles of marginal stream habitat." Expressed as a proportion this establishes a target of 34 percent excellent, 48 percent good, and 17 percent marginal. To be in attainment the proportion of both excellent and good needs to exceed the respective targets of 34 percent and 48 percent or the proportion of excellent needs to exceed 34 percent and the combined proportion of good and excellent needs to exceed 83 percent (34+48 percent).

As of 2022, the stream mile condition is 34 percent excellent (in attainment), 44 percent good (somewhat worse than target), and 22 percent marginal (somewhat worse than target), therefore, the status is somewhat worse than target.
Little or No Change. The average California Stream Condition Index (CSCI) score of two panels of trend data (A and B) have been analyzed over all the evaluation periods. To determine trend, the average CSCI score for the trend panel data for each reporting period is assessed. The long term trend line shows a negligible change in annual mean CSCI scores per evaluation period, with a slope of -.0016 for Trend Panel A and -.0087 for Trend Panel B. Therefore, a trend of little to no change was determined for both trend panels.
Confidence Details
High. Standardized California statewide protocol is used with a data set back to 2009.
High. Confidence of trend is determined by the duration of trustworthy data and both the coefficient of determination and t-test significance. There is a long term trustworthy dataset. Trend confidence for Trend Panel B data has an R²= 0.95, (high) p-value= 0.003 (high). therefore, the confidence of trend is high.
High.
Additional Figures and Resources

No photos available.

No documents available.

References

SEZ Baseline Condition Assessment - An assessment of the current conditions of Stream Environment Zones (SEZ) throughout the Lake Tahoe Basin. Tahoe Regional Planning Agency - Funded through a United States E.P.A. Wetlands Development Grant. December 15, 2020.