Random lag spikes any time processor intensive tasks a scene

This issue has been pestering me for a while now, and I can't seem to find a solid reason for why it's happening. Here's the gist of what is happening: whenever I put processor intensive elements in any of my scenes - whether it be reflective water, Tenkoku dynamic sky, or just a bunch of cubes in an area - I'm getting random spikes of lag followed by smoother gameplay. These lag spikes will continually pop up, and then revert back to the normal framerate.

I fully understand that as you tax the processor more it will reduce the framerate. That's fine, but not really the problem. The problem is the sudden framerate dropping followed by returning to the normal framerate. Often times it freezes the game for a little bit and then continues as normal. Very distracting for players.

I can provide information for particular instances, but the issue seems to be with any thing I do. If someone can point me in the right direction at least, or offer info about this/a similar problem that would be appreciated.