Go out later in the morning,( crappie are somewhat lethargic early morning due to feeding in the cooler pre-dawn hours). Bites seem to pick up closer to 10:00 or so for me. I fish a shallow, pretty murky lake. Don't hesitate to fish very shallow water, (5 or less). even with 90 degree water temps. If the baitfish are there the big crappie will be there also. You won't find too many dinks this shallow as these waters are full of cruising gar too.
Unless you're extremely skilled in stealthy boat control while Livescoping, a casting technique of some sort will probably be more productive and spook less fish. Spiderrigging with long poles, preferably 14 feet or longer, would probably work well too.
One last thing is comfort in the boat while fishing the summer heat. I have a Millineum Umbrella holder on a spare seat post that I can switch to a hole on either side of my center seat position. I use an inexpensive 6 by 7 foot rectangular umbrella from Walmart. I can also adjust the umbrella to lean back away from me for low sun conditions, I also use it on favorable weather days to just shade my electronics to see my screens without glare. Works great! I have a half-gallon Igloo jug I fill completely with ice then filtered cold water from the fridge. It stays right by my feet all day. Probably the single most important thing that allows me to fish in this intense heat is an 18 volt Ryobi Fan. I put it on the floor right in front on my right side. I angle it almost straight up on me.
A week or so ago I started about 10:00 AM and fished most of the rest of the day in 108 heat index and no wind. I was extremely comfortable and managed a nice limit of summer time slabs while having the whole lake to myself. I was watching boat after boat running to the ramp and leaving by 11:00 as the heat was bearing down.
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