Woody -
Separating summers and winters; especially at this time of year can be difficult. The most reliable method on the Skykomish as well as most Puget Sound rivers (especially for the hatchery fish) is to look for parasitic copepods. This lice-like parasites attach themselves to the fish during the summer. Usually you can find them in the mouth (roof most common location), on the gill rakers, and at times at the base of the fins (most commonly the pectorals). The parasite is about the size of a grain of rice with a whitish to tanish coloration. Each summer ususally has a hand-ful to dozens of these parasites.

For fish that have been killed looking at the entrails also can helpful. The summer fish have generally exhausted their fat reserves thus will have paler flesh than a winter fish. Locally hatchery winter fish begin spawning in December where summer fish begin in January. Therefore this time of year "ripest" fish will be hatchery winters - not summers.

Things can get complicated - for example it is not uncommon to see summer fish on the lower rivers this time of year. Some of those fish will have copepods- however they will be dead (paler in color and beginning to shrivel). These fish have been in another river (say the Stilli) dropped out to the salt (kill the parasite) and then re-entering another river (Snohomish).

As you know this time of year it is common for a bunch of fish to show up at Reiter (especially following the first big rains). Most if not all of these fish are not fresh run fish but rather summer fish that have been scattered throughout the river (mostly upstream of Reiter) that are returning to "home" with the river rise. Except for the rare winter fish they are not just entering the river.

Tight lines
Smalma