I have started this reply more times than I can count and every time I have been interrupted before I can finish it and post, sorry.
First things first, yes, raking leaves and debris from the lakebed is considered dredging and is a regulated activity under RSA 482-A. (
For those who may be curious please feel free to check out RSA 482-A:3,I, (a) and RSA 482-A:21 - 25,
http://www.gencourt.state.nh.us/rsa/.../482-A-mrg.htm.)
The NHDES has through adopted rule, created a permitting exemption for the raking of leaves in the dry from areas of lakebed that are exposed due to drawdown or, more recently, drought (
see Env-Wt 309.02(f)).
If the area of lakebed in question is going to be submerged during the leaf removal project, the least environmentally impacting way to accomplish this is raking. One should try to do this work when there is as little wave action as possible. A turbidity curtain should be installed to contain the sediment that will get stirred up until it can settle out. (
Think tarps weighted to the bottom and perhaps held up vertically by something like yard/garden stakes.) Done this way, yes, the project removes habitat for macroinvertebrates that are an import base of the food chain and also some of the critters themselves, but it minimizes the introduction of nutrients into the water column, it minimizes the area the sediment settles back onto, and it minimizes the area in which aquatic species will be taking the suspended sediments into their gills.
Adding nutrients into the water column leads to the algae blooms that no one here seems to enjoy. When organic debris and silt settles to the bottom it can contribute nutrients to plant and algae growth but this contribution occurs very slowly. Stir this material into the water column and it spikes the nutrient loading and growth can explode. It's like combustion; it's all about fuel to air ratio. In addition, when the stirred up sediment settles onto areas outside of the dredge area it can suffocate even greater numbers of macroinvertebrates as well as eggs in finfish nests leading to completely unnecessary and avoidable fisheries impacts. These are the reasons that containment during the project is important. These impacts are all maximized when one uses any type of "blower" to relocate their leaf problem.
So please, before using your waverunner, prop, aquatherm, "muck blaster" or any or commercially available system to "blow" leaves out of your swimming area, consider that you may just be moving your problem onto your neighbor and more importantly you are doing it in the single most damaging way possible. Please, choose well...