I agree with the PT sill however if you live by the lake there are much better choices for the walkway than PT.
PT has improved over the years regarding environmental issues but IMO still has stuff in it that one would not like leaching into the lake. It all adds up, a little fertilizer here, a little PT there, a septic issue etc... it all affects the water quality and aquatic health.
When your current walkway needs replacing consider a product such as trex, the extra cost is minimal and the use of this product should give you peace of mind that you are not doing harm to the environment.
