"Full pool" is the operating-agency's target elevation for a reservoir during its normal management cycle. For a flood-control reservoir, it's the top of the conservation pool — water above this level is held only briefly during storms before being released through the dam. For a water-supply or hydropower reservoir, it's the typical maximum the operator aims to keep the lake at during the recreation season.
On Lakebrief, every reservoir entry stores its full pool in specs.fullPoolFt. The water-level chart's percent-full readout is calculated against this value. A reading of "100%" means the lake is at full pool; lower percentages indicate drawdown.
The number is published by the operating agency and varies by lake. A few examples from the Lakebrief catalog:
- Spruce Run Reservoir (NJ): 272.4 ft NGVD29, per the New Jersey Water Supply Authority's December 2024 operations report.
- Lake Lanier (GA): 1,071 ft (summer), 1,070 ft (winter), per USACE Mobile District. Winter pool is one foot lower to provide flood-storage capacity ahead of spring runoff.
- Lake Tahoe (CA/NV): 6,229.1 ft, the federal "maximum legal limit" set by the Truckee River Agreement. This is unusual — most reservoirs aren't bound by a multi-state legal compact.
"Full pool" should not be confused with "flood pool" or "spillway elevation." Most reservoirs can hold water several feet above full pool during a flood event before water reaches the dam's spillway and discharges over it. Lake Lanier's flood pool tops out around 1,085 ft — fourteen feet above full pool. The dashboard's percent-full scale ignores the flood-pool zone because no reservoir is operated there for any meaningful length of time.
For natural lakes (Hopatcong, Lake Mendota, Lake Washington), the same field stores the typical managed surface level — usually a target elevation set by a regulating agency that operates an outlet structure on the lake's outflow.