I have read answer by @John Rennie in regards to the size and density of black hole. In the last sentence he states that super supermassive black hole
with the mass of 4.3 billion Suns would have a density equal to one i.e. the same density as water.
Does that mean that there is a limit to the size of black hole? (otherwise I should be able to swim in it). What am I missing here?