The way I see it is that on the outgoing tide, any fish in the river part and at the mouth, the water level drops, and fish are more "congested", and you can cover more fish with a single cast...or at least that's my logic.
ok, that explains low tide being better.
I have since done some reading, and as far as fishing during tide (or around tide) vs. fishing when the tide is not happening.... this is what I read:
"A: Joseph, when we talk about fishing the tide change what we're referring to is one hour before to two hours after the high or low water period. The reason fishing is better then is salmon don't like to expend any more energy to capture food then necessary. During the high and low tide changes salmon can feed when there is little or no current to contend with making it less work to attain the same amount of food. Capt. John"
Of couse, I have also read just the opposite of the above