No won't kill the lake, but will be a major nuisance
the lake will eventually be infested, and the main problems will be:
- Boats left in the water. The mussels, in large numbers, will attach to the hull and prop. Similar to barnacles, but possibly worse
- Swimmers/waders - The mussels are sharp and can cut your feet
- Outflow pipes - Probably the biggest hazard, they will infest and clog up pipelines that bring water to cities
The good news is water clarity will improve, so there is that.... But that may be a symptom of conditions that could be harmful to some species
So, if you're a lake goer, you're just gonna have to learn to live with 'em