The dog days of summer are here and it is time to change strategies for whitefish. Being a cold water fish, the whities need to hole-up in deeper, cooler water at this time of the season. They also become a bit slower in their feeding. This means that you have to offer the bait to the fish in a slightly different manner.
Many lakes have deep holes that you can find either with sonar or topographic maps. Once you are over one of these holes, you can check to see if the whitefish are present. Sonar is the fastest, easiest way to do this. If you spot fish near the bottom in the hole you can be sure that the specie is walleye, trout, or whitefish, as these are the three most common sport fish to use the colder parts of the lake in summer. Having a GPS is also beneficial as you can mark these spots for future trips or as a starting point for winter fishing.
Chumming.
Sometimes you have to chum the whitefish in to the area you are fishing. This is not a big deal and will attract the fish for as long as you keep the chum on the bottom where you want to fish.  Try using salted minnows if they are allowed on the lake you are fishing. Cut-up minnows work just as well, but will sour if not cleaned up within a few days by the fish.
A bottom-baiter is the easiest way to get the gait to the bottom without it spreading over a large area. You can make one out of a funnel by placing a weight in the spout of the funnel; a bolt with a nut and washers will do nicely. Make sure you place a large snap swivel on the outside of the spout so you can hook this to the line you use to send it down with. Always send a line to bottom first with a good-sized weight so it will go straight down below your boat.

Place the bait in the funnel and hook the snap to the line. Carefully place the funnel in the water and let it fill slowly. The bait should be pushed down so it will not float up and out. A small lid can be used for this but be sure to make it easy to open. Hooking it to the funnel with a small piece of wire should do the trick. Now let the funnel fall freely until it hits bottom. After you feel the weight of the bottom baiter hit the bottom start to retrieve the line with the funnel attached. As the funnel turns over in the water all the bait will slide out and stay directly under your boat, unless you have a strong bottom current, in witch case you should bait up current.

Live Baits.

The most common bait for whities, are a live minnow. If they are allowed in the lake you are on, try them first. Hook the minnow so that the hook is placed from the underside of the minnow and facing back towards the tail. (Be careful not to enter the white spot, or belly of the minnow. As this will cause the minnow to die.) Place the minnow in the water and see the action it makes as it tries to swim. The minnow should look lifelike and be right side up. I like to use a two way spreader for this application and I will let it rest on bottom. Either a small float can be used to detect a bite, or you can simply let the line sit slack for a moment and then lift lightly. A bite will be detected when lifting, as the weight of a fish will be felt.

Whitefish have a thick upper lip and will hold a hook well if not too much pressure is applied on the retrieval.

Worms can also be used, but try injecting a small amount of air into the worm to keep it about an inch or so off bottom.

White grubs are another favorite of the whitefish.

Spoons.

Williams Whitefish Junior, Little Cleo, Swedish Pimple are the most common.

If you choose to use a spoon to catch these tasty fish, then you should start with something like a Williams Whitefish Junior. Either a plain silver, or half-and-half.

To use the spoon, try letting line out until the spoon is on bottom. Now reel in just enough line so that you can feel the weight of the spoon and start a slow jigging motion. Let the spoon hit the bottom on the down stroke and lift about six inches off bottom on the upstroke. This causes the spoon to rile the bottom slightly, imitating the look of feeding baitfish. This will in turn cause the whitefish to feed on the baitfish. The spoons can be used as is or tipped with a live minnow or a part of a minnow. Garlic seems to draw these fish and I always rub a bit on my hands before handling the line or bait.