Yes, there is a great deal of spawning that takes place there. The Salmon and Brook Trout at East Outlet are for all practical purposes, native and resident river and lower impoundment dwellers in Indian Pond; have been for years, along with Togue, or Lake Trout, Sculpins, Dace, Crayfish, Bass, Leeches, Bugs, and..... Smelt, which is the key-on forage fish for fly rodding for Salmonids in spring and late fall.
There are abundant gravel areas, some of which have been enhanced by fisheries management for spawning Salmon and the East Outlet section of the Kennebec River supports natural reproduction, perhaps as well as any river in the Northeast part of the USA. I love it there. Mid-October. Water at 50-degrees or less.
Weather can be brutal, with storms, rain, cold, especially in late October, but the fishing that goes along with that can be like no other in the East when the Salmon kypes enlarge, Brook Trout are in full colors, and fast-stripping a streamer fly is the game.

I love those times when fish are on the bite aggressively.
What's your favorite fish to fly fish for near Naples, Mark? Tarpon?