Where did I set my horse last night...

The Assassin's friend...

1,000 feet seems really weak for a 4th level locate spell. That's 1/5 a mile.

I reckon you could get the DMs permission to increase the range. 

So basically you can see it(if u are up on a watch tower or something)

Is there a specific reason for the limitation "This spell can't locate a creature if running water at least 10 feet wide blocks a direct path between you and the creature."

I find it particularly puzzling.

I thinks its almost a joke because crossing a river is a way to cover your tracks/smell? The material component is a bit of fur from a bloodhound. Idk id personally remove that limitation as a DM.

Quote from ZachNoorman >>

Is there a specific reason for the limitation "This spell can't locate a creature if running water at least 10 feet wide blocks a direct path between you and the creature."

I find it particularly puzzling.

 I agree

Lord of the Rings: The Fellowship of the Ring

How vague a description can it be?

My character is hunting down their families killer, they don't know who they beyond the fact are they're a wizard, if my character cast this spell to find "The wizard who killed my family" would that work?

The "This spell can't locate a creature if running water at least 10 feet wide blocks a direct path between you and the creature." part seems highly limiting considering just how narrow 10ft is. Surely there are rivers and creeks in a lot of places. The fact that it does have to be running water is a bit helpful though.

So does the second part of this spell have the same distance limit? It kind of sounds like if you are tracking a specific person in the first paragraph it has to be 1000ft but the second makes it sound like you can tell the position anywhere as long as not blocked am I wrong? 

It does specify that you had to have seen a creature within 30 feet to track it. I would rule they would have had to have met the person to use the spell to try and find them. 

I don't think the second paragraph is defining a separate ability, just clarifying the first paragraph. Clarifying that you can target a specific or general creature and that it only reveals the closest creature, not all creatures of that type within the radius. The range limit would still apply according to RAW.

Quote from ZachNoorman >>

Is there a specific reason for the limitation "This spell can't locate a creature if running water at least 10 feet wide blocks a direct path between you and the creature."

I find it particularly puzzling.

 Most divination spells have some sort of limitation built in. It's both to give the DM an out if they don't want the spell to work, and a way for clever players to avoid being detected.

Lorewise, I'd agree they were reaching on this one. The lead sheet mentioned in other spells makes more intuitive sense, but isn't practical for a creature, so I guess this is the best they could come up with.

Quote from Gavros963 >>

How vague a description can it be?

My character is hunting down their families killer, they don't know who they beyond the fact are they're a wizard, if my character cast this spell to find "The wizard who killed my family" would that work?

My take:

If you were looking for a black cat or a human with blond hair, I'd probably be fine with it finding the nearest of those. If you saw the culprit, I'd probably let you find that specific person by description even if you didn't know their name (maybe I'd require you to have been within 30 ft of them, though).  But I would disallow specifying them based on their past actions. I'd probably disallow a description like "a wizard," too.  If the spell was meant to be that powerful, I think it would have been much more explicit about it.  I *might* allow "a human dressed like a wizard," but that might be opening a can of worms... Not sure.

Some other fun ones I wouldn't allow.  😁

"Find the nearest human living in a universe where it is possible to prove the Goldbach conjecture."

"Find the nearest dwarf who will lend me five bucks."

"Find the nearest creature who can't be found by this spell."

I think I would allow "Find the nearest human with six fingers on his right hand," though... ⚔️

This really seems a lot weaker than locate object. Unless you are looking for a specific creature like an owlbear. Even then, a dm could just rule that you could choose something like an owlbear beak or pelt with locate object.

Running water is a good way to wash away your scent to make it harder for you to be tracked. It also blocks certain magical creatures - Dracula, for example, had to wait to board and disembark from ships until the tide was perfectly between ebb and flow, because otherwise the flowing water trapped him.

Something I’m wondering is, if you meet a creature that’s polymorphed into something else, and then try to detect it while it’s still polymorphed into that shape, does the spell fail?

I know you're question is a bit old but here's how i look at it:
"If the creature you described or named is in a different form, such as being under the effects of a polymorph spell, this spell doesn't locate the creature."
As a DM I would interpret this as "Different from when you met them". I don't think its a case that the spell can tell that someone is polymorphed or not, but rather that it is trying to match the creature to how you know them i.e. 'You met a human, spell looks for a human' or 'you met a bear, the spell looks for a bear'. (Lets be frank, if the spell could tell if something was polymorphed or not it wouldn't fail)
In your example "you meet a creature that is polymorphed" and "while it's still polymorphed" I would rule this that they match the image that you know them to be and such the spell would work. I would even go so far as to say if they get polymorphed again into the same form, the spell would succeed because they Currently match the form you are looking for.