Sorry that I don't have too much information for you on this. The site that I was linking to for this event has not been updated and the dates are wrong so I threw this together quickly. There are a few things I can tell you though.
- These are some of the best fireworks I have ever seen, however, the weather is unpredictable. They don't get rained out but it can be uncomfortable watching in the rain or fog.
- If you decide to make the trip, you should plan on going early as there are shows and activities throughout the day.
- The festival takes place in Yasumiya. This village in on the south side of the lake.
- At dusk, the lake ferries begin converging and they are all lit up. This adds to the colorful displays of the fireworks which begin at 8pm.
- The only drawback is the drive home. Expect a lot of traffic and a longer drive than on your way out there.
I have driving instructions
here