A. Answer: You've asked a question that would take many, many pages to respond to, depending upon the detail you wanted to go into. What I will do is list some of the important physical attributes of streams and how they affect spawning activity.

1. Substratum particle size: For successful spawning, trout must find places in the streambed that contain the right sized rocks for them to build their nests. This is usually gravel sized, although bigger fish can obviously excavate larger materials. They need to find a site where they can dig their nest and then, following oviposition, bury the eggs.

2. The right size gravel is also important for providing large enough spaces for the water to continually flow over the developing eggs. This provides well-oxygenated water for the eggs and also sweeps away metabolic wastes and silt particles that could smother the eggs.

3. This water flowing over and through the nest must contain adequate oxygen for the developing embryos.

4. Successfully spawning also require silt-free water so that the egg nest will not become covered with fine particles that will preclude the oxygen-bearing water reaching the eggs and result in effectively smothering the eggs.

5. The right size particles and interstitial spaces is also important because when the embryos first hatch, they spend their early developmental period living in these spaces while they absorb the yolk sac prior to beginning active feeding.