At the very least a priest must be able to see the water they are blessing. The rest starts to come to denominations etc. however-
1. Roman Catholics require the water being blessed be FRESH water. No oceans.
2. Many denominations require that water ONLY can be blessed in a designated sacred area- a church, a specific part of the church etc. so a large body of water, or any water not in that place couldn’t be blessed.
3. Most denominations require the sign of the cross be made over the water. 4 points end to end. That would make blessing a large body of water very difficult if not near impossible.
Now- here comes the kicker. This is pretty universal across denominations. So even where the others don’t apply or can be wriggled out of- this one is the topper.
MOST RELEVANT FACT:
“Holy water” is consecrated water. It is generally part of sacrament. A priest may only create holy water for use as such. That means- a priest can’t just turn any water holy. It must be made holy for specific purpose of use in the religion. It also must be treated as sacred. You cannot make a bath of holy water because bathing isn’t allowed in holy water. You can’t turn a lake or ocean holy because you can’t play or pee or poop or any of the other things done in public lakes and oceans with creatures in them: in holy water. Not only can we argue that by violating this (or any other rules that apply to their faith) the water wouldn’t be “holy water” even if blessed as such- but it’s use in sacrilege would defile the holy water and it would no longer be holy water. Just water.
Tl:dr- in most major denominations even the pope cannot make all water holy or huge amounts of holy water. The water must be intended for use in a sacred capacity and to be holy it must be treated holy. That which is profane (or can’t be done in church) can’t be done or with that water. There are some VERY limited and unlikely scenarios that could allow a lake etc. to be made into “holy water.” There are also limited cases where some body of water may be considered holy but that generally relies on a history with a saint or prophet or messiah or God and not just a pope or priest.
The short answer is that they can bless at least all the water in sight and potentially all the water in the body of water but that would inevitably result in its misuse so they are not allowed to.
1. Roman Catholics require the water being blessed be FRESH water. No oceans.
2. Many denominations require that water ONLY can be blessed in a designated sacred area- a church, a specific part of the church etc. so a large body of water, or any water not in that place couldn’t be blessed.
3. Most denominations require the sign of the cross be made over the water. 4 points end to end. That would make blessing a large body of water very difficult if not near impossible.
“Holy water” is consecrated water. It is generally part of sacrament. A priest may only create holy water for use as such. That means- a priest can’t just turn any water holy. It must be made holy for specific purpose of use in the religion. It also must be treated as sacred. You cannot make a bath of holy water because bathing isn’t allowed in holy water. You can’t turn a lake or ocean holy because you can’t play or pee or poop or any of the other things done in public lakes and oceans with creatures in them: in holy water. Not only can we argue that by violating this (or any other rules that apply to their faith) the water wouldn’t be “holy water” even if blessed as such- but it’s use in sacrilege would defile the holy water and it would no longer be holy water. Just water.