Depending on what you mean by "the speed of light", it's quite easy. The speed of light in water is 0.75c, but other things sometimes travel faster than that i

Depending on what you mean by "the speed of light", it's quite easy. The speed of light in water is 0.75c, but other things sometimes travel faster than that in water -- Cherenkov radiation (the blue glue in reactors) happens when you have eg electrons moving through the water at speeds faster than 0.75c.