I would try pond dye at ice out in the spring or this fall, try to get your water clarity down to less than 36" if you can. Apply the dye conservatively, you do want some light penetration to feed an algae bloom. Add dye as needed later on.

Vegetation needs these three things to grow well:

1. light
2. nutrients
3. the right temperature

Take away any one of those three things and aquatic vegetation won't grow well. Reducing the amount of light the vegetation receives is a simple remedy.

Navigate does work well but it is expensive and has to be done every year, at least that is my experience. My dad's old pond also had issues with milfoil and coontail. I like clear water but it can really let the aquatic vegetation get out of control.

Are the any oak trees around the lake?