By a lot, mostly. The liquid hydrogen eventually doesn't have enough pressure/cold enough temperature to stay liquid so it turns back to gas and most bubbles out of the water (with some of it reacting with Oxygen and becoming more water). It's possible if it were a "big enough" and "concentrated enough" spill it might briefly create anoxic zones where fish will die. https://en.wikipedia.org/wiki/Anoxic_waters (But humans and dumb algae accidentally do that "all the time" and the ocean does have recovery methods from anoxic waters. It's not great for the climate or the ocean, but it is mostly survivable and much more "temporary" problem than the long term effects of oil pollution.)

It is also a greenhouse gas http://agage.mit.edu/publications/global-environmental-impac...

"If a global hydrogen economy replaced the current fossil fuel-based energy system and exhibited a leakage rate of 1%, then it would produce a climate impact of 0.6% of the current fossil fuel based system. "

That doesn't sound so ... bad?

The hydrogen goes up. Most of it will be in space in an hour or two. Any that doesn't will react with atmospheric oxygen to produce water vapor.

Maybe ever so slightly acidifies water + escapes atmosphere; I don’t think there is real hydrogen spill pollution.

Sure, but it's not a big concern as it's not that common.

To the person who disagrees - compared to climate change, it's the least of our worries.

No oil spills beats a few oil spills - but these are not an Exxon Valdez sized event, and they don't really matter in the grand scheme of things.