Measurement methodology

Levels retain the provider’s native units, calendar dates, statistic, quality and water-surface reference. A daily observation is not a daily mean. The latest available value is not labelled live.

Freshness and completeness

Measurement age is recalculated on each request. Daily records are stale after seven provider calendar days; timestamps retain their original offset. If the time zone cannot be resolved, freshness is unknown. A failed refresh preserves the last available measurement and its original date.

A provider-reported daily mean does not establish that all expected samples exist. Sampling-complete means are suppressed when completeness is unverified. Exact-date differences between eligible provider-reported daily means remain available with an explicit sampling-completeness qualification. Approved and provisional describe provider quality, not sampling completeness.

Changes and historical context

One-day and seven-day changes require observations on both exact dates, eligible quality and the same series, water datum and known operational regime. Missing dates are never interpolated or replaced by a nearby date.

Prior-year comparisons use the exact month and day within the fixed January 1, 2006–December 31, 2025 reference interval. The actual eligible years and sample count appear on each page. The captured series begins in 2024 for this release; it is not a complete twenty-year record or a seasonal norm.

Percentiles are disabled in the frozen methodology. The declared quantile method is Hyndman–Fan type 7; at least ten distinct eligible years would be required under an approved future qualification. February 29 percentiles remain suppressed.

Extrema and charts

Minima and maxima use eligible original daily values in the displayed date window. All tied dates are retained. Missing days can conceal more extreme values, and an incomplete year is labelled. Daily-mean extrema are not instantaneous or all-time records. Provisional and revised observations may change results.

Charts retain first, minimum, maximum and last values in display buckets. Missing, invalid or incompatible observations break the line. This reduction is for display only; calculations and the accessible history table use original values.

Datum, units and corrections

Incompatible datum or series segments are excluded from combined comparisons. Unit conversion does not transform a vertical datum. Where the provider’s foot subtype is unestablished, native feet are displayed without conversion. Decimal places follow source reporting and do not imply measurement accuracy.

Refreshes reconcile provider corrections into a new version of the lake dataset before replacing the active version. The downloaded CSV includes statistic, units, series, quality and source provenance.