Here is a short video showing some of the advantages of being prepared with a few different sinking lines during the warmer months of the still water season. Sinking lines can be utilized throughout the entire season to search low lying fish, just off the bottom. Most individuals that choose to troll flies for Trout in lakes will find sinking lines to their advantage. For superior casting / searching methods, all the normal types of sinking lines will work very favorably from anchoring in shallow waters and casting and retrieving to deep drop off / darker water zones.
The higher the number of the "type" of sinking line, the faster the sink rate. Type 1 is intermediate (very slow, best purchased in clear). Type 3 is medium sink (most low end generic sinking lines are type 3 although high end lines are available) colours may be dark green, dark blue, brown or black. Type 6 or 7 (extra fast sinking, normally black) mostly produced in better series of fly lines.