A handful of US state parks publish a documented sustained-wind cutoff that prohibits boating once exceeded. It's not a guideline — it's a regulation, enforced by park staff. The most prominent example is in New Jersey, where the regulatory text reads:
"A person shall not continue boating activities on Spruce Run Reservoir when the wind velocity reaches or exceeds 25 miles per hour."
— NJ Administrative Code 7:2-8.8(a)
NJ DEP applies the same threshold to Round Valley and Hopatcong. Once sustained wind hits 21.7 knots (25 mph), boats must return to shore; new launches are prohibited. The rule exists because both reservoirs sit in steep-walled valleys where afternoon thermals can ramp 5 → 25 kt in minutes, and historically the park has handled multiple capsize incidents in those windows. The numeric threshold gives rangers an unambiguous decision rule rather than a judgment call.
Other agencies operate differently:
- USACE-managed reservoirs (Lanier, Monroe, Canyon Lake, Table Rock) follow federal 36 CFR Part 327, which doesn't include a sustained-wind boating prohibition. They post safety advisories when the NWS issues a Lake Wind Advisory but don't legally prohibit boating.
- City of Oklahoma City (Hefner) has no documented sustained-wind rule.
- Denver Water (Dillon) has no documented sustained-wind rule, but does have a 30-mph boat speed limit and enforces a no-PWC policy.
Lakebrief encodes this distinction in each lake's parkRules.windLimitKt field:
- Hard rule lakes (NJ DEP): set to the documented prohibition, currently 21.7 kt. The sailing score hard-zeros above this threshold, and the alert ribbon surfaces a "Park rule: no boating" message.
- Soft cap lakes (everywhere else): set to 30.0 kt — roughly the gale-warning band. The score curve still degrades smoothly toward zero at extreme wind, but the message reads "small-craft advisory" rather than "park rule," so the dashboard doesn't fabricate a rule that doesn't exist.
The Phase 2 architecture roadmap includes splitting windLimitKt into hardLimitKt and smallCraftAdvisoryKt so the score curve and alert copy can adapt independently. For now, the single-value model is the right trade-off for the catalog's current size.
If you sail at a lake with a hard rule, treat the dashboard as one input — the on-site ranger has final authority. If you're at a soft-cap lake, the dashboard's threshold is advisory; your skipper judgment governs the actual decision. Either way, the threshold is documented in the lake's source file with a citation to the regulation, so anyone can audit where the number came from.