Pic 1 is scattered fish in the water column with a few rising toward the boat as they pass thru the sonar cone ...
Pic 2 is the same as 1 .. but also with possible brush on the lake bottom ...
Pic 3 is the same as 2 .. but with a single brushpile on the lake bottom ...
Pic 4 is scattered fish in water column and definately thermocline at 40ft and deeper ...
(notice in pix 1-4 how the length of the fish arch is affected by the boat speed = slower boat speed allows the fish to stay in the Sonar cone longer to create longer echoes on the display)
Pic 5 is misleading because the 999 SI unit doesn't actually have a DI piezo ... the DI image is created from the data received with the SI piezoes and computer generated to "look like" a DI image ...
So even tho the "mass" looks like it's reaching from the surface to the bottom ... it's actually reaching from the boat's path out to the side (and it's most likely your boat passing thru your own prop wash or another boat's prop wash) ..
It would help you understand this by opening a Combo SI/DI view and purposely drive thru your own prop wash at an angle and see how the prop wash is displayed in SI vs DI ...
Rickie