Stihlhead-
No need to name the creek or email me that information - don't want to tread on anyone's zipper-lip. I was not sure whether the "creek" was open to fishing or some small tributary you had encountered in your travels.

In the Puget Sound region the hatchery winters spawn from late December to late February and the hatchery summers spawn from mid/late Janaury to early March so it is possible for the two to cross. The wild summers and winters use different portions of the basin so are unlikely to cross.

In the wild whether a fish population is a summer or winter is largely determined by the types of habitats the fish lives in and what strategy is most successful of over the generations. Both fish are late winter/spring spawners. Thus we tend to find summer fish on systems were long migrations (hundreds of miles) are needed or in upper sections of shorter systems were there are falls or canyons that the are difficult migration points that are most easily passed in summer/fall flow conditions.

A cross between a summer and winter fish is likely to procduce a "tweener" - a fish with the characteristics of both. This implies that such fish would be a fall type fish. Clearly the stream where you saw the fish was naturally a winter run stream (enough clues to guess which stream) such "tweeners" would
likely be less successful in the wild so their offspring would have low survival (not matched to their habitats) and unlikely to persist for long.

Tight lines
Smalma