It is unlikely that you will be able to resolve this amicably unless your neighbor pays to replace the evergreens and shuts down his pool.Nuisance is an unreasonable interference with the use and enjoyment of your property.You can sue your neighbor for nuisance and seek damages (monetary compensation) for the loss of the trees and the damage to your property from flooding your yard.However, damages are an inadequate remedy due to multiplicity of lawsuits since the flooding is continuous and also because land is unique.  Therefore, since damages are an inadequate remedy, you can seek an injunction against  your neighbor to stop the flooding of your property.