July Heat Is Not Summer Peak

The freshwater home screen used to call July a summer peak.

Maximum metabolic rate. Fish feeding aggressively. The pill sat under the score and told you the season was on your side. For a generic target, in warm water, that sentence is often fine. For vendace it was a lie.

Vendace (Coregonus albula) are a coldwater fish. Their useful temperature band in the app sits around 6 to 12 °C. Peak months are winter and late autumn, not the holiday fortnight. Put them in 18 °C water in mid-July and they are not at a feeding peak. They are above their range. They hold deep, or on cooler inflows, with little surface activity.

The calendar had no way to know that. July was summer. Summer was peak. The species was decoration.

A month is not a metabolism

Fish do not share a season.

Pike can be on the beds in February and March if the water is in the spawn band. Zander can be in an active summer window at 20 °C. Vendace at the same date, in water that would thrill a carp, are looking for cold. Char and other coldwater fish fail the same way if you let the month speak first.

Spawn is the other trap. A spawn calendar is not a bite forecast. Fish on the beds are busy. The honest labels are pre-spawn, spawn, and post-spawn, with the temperature gate attached. "They are spawning, so they must be hungry" is the same category error as "it is July, so they must be peaking."

The phase has to come from thermal guild, the species temperature band, and the spawn calendar, in that order. The month is a fallback when you have no species.

What thermal refuge means on the water

Above the range, a coldwater fish does not vanish. It compresses.

Surface water is the wrong place. The useful band is deeper, on the thermocline if the lake has one, or on a creek mouth that is still feeding cold water in. Retrieves slow down. Topwater theatre stops. You are not fishing a peak. You are fishing a refuge.

That is a different day from a warmwater predator in the same lake, on the same afternoon, using the same weather. One species in thermal stress looks for shade and low light. The other is still on prime structure. A single "summer peak" pill cannot describe both.

We tested the old path against vendace at 18 °C in mid-July. The generic path still said summer peak and talked about aggressive feeding. The species path now says thermal refuge and points deep. Same water. Same date. Different fish.

What we changed

The freshwater verdict is species-aware. Thermal refuge and thermal stress sit in the phase list with pre-spawn, spawn, summer peak, and turnover. Coldwater fish above their range get refuge copy, not a peak. Warmwater fish in range still get a thermal-fit peak, without the generic "maximum metabolic rate" line that used to cover everyone.

If there is no species, the old calendar path remains. That is the honest limit. A general target cannot pretend to know a guild.

This is not a claim that every lake is stratified, or that 18 °C is a universal vendace shutdown. It is a claim that the month is a weak author. The species and the water temperature write the phase. When those disagree with the calendar, believe the fish.