A pressure washer is a tool used to remove dirt from various surfaces such as buildings, roads and vehicles. It uses high pressure water combined with a mechanical sprayer to do the job. They can be bought or rented and typically use cleaning solutions during its operation. To simply use a power washer with lake water is impossible, as the impurities and the varied flow of the water would break the pump. The simplest way is running it from a faucet which uses filtered lake water, but that is not always possible.
Purchase a submersible pump or a well pump from a specialty store or online distributor. Install this in the lake following the instructions in the manual or have it professionally installed.
Run a hose from the pump to the location where the power washer will be used. The length will depend on the distance of the two locations, and the width of the hose on the actual make and model of the well pump.
Purchase a water filter system and install it. These are available in any department store and come with all of the needed parts. Double check whether the filter is included as that might have to be bought separately.
Run a second hose from the output of the filter into a faucet. This can be a regular faucet or one with a knob, but it needs to have the option of turning the water on and off as otherwise it will continue to run and be impossible to control.
Hook up the hose from the power washer into the faucet. Turn on the power washer to be able and use it with lake water.