Tie on a white lure that sinks, such as a spinnerbait.  Drop the lure into the water. 

If you cannot see the lure after it sinks 1 foot, the water color is very muddy.

1 to 2 feet - Muddy

2 to 3 feet - Stained/Muddy

3 to 4 feet - Stained

Over 4 feet - Clear

Over 6 feet - Very Clear

Understanding water clarity will help you choose the best lures and the best lure colors.  Typically, when the water is on the clear side, you want natural colors such as green pumpkin, pumpkinseed, or white.  When it is stained, you want blacks, blues, purples, chartreuse, orange, and brown.  Colors such as brown and pumpkinseed can be effective in both clear and stained water.

Water clarity also affects lure selection.  Crankbaits and spinnerbaits are most effective in stained water.  When the water is stained or muddy, lures with rattles are effective.  However, in clear water, rattles may be counter-productive.  If the water is muddy, a jig in black, blue, or brown may be a better choice than a spinnerbait or soft plastic.  When selecting a spinnerbait, use a Colorado blade in stained or muddy water and in clear water, use a willowleaf blade.  Nickel colored blades are usually better in clearer water and gold colored blades are usually better in stained or muddy water.

These are general guidelines that you can use when starting your fishing day.  Using these guidelines, you can save time when you are trying to narrow down a pattern for the water conditions you are fishing.