Si encontramos una charca, mi hija va a mirar si hay una mosca sobre el agua.

After si meaning if, Spanish normally uses the present indicative for real or possible future situations:

• Si encontramos una charca... = If we find a pond/puddle...

This is one of the big differences from English. English also uses a present form here (if we find), but learners sometimes expect a future or subjunctive in Spanish.

Compare:

• Si encontramos una charca, ... = if we find one
• Si encontráramos una charca, ... = if we found one / if we were to find one (more hypothetical)

So encontramos is completely normal here.

Because the two si words do different jobs:

1. Si encontramos una charca
   Here si means if and introduces a condition.

2. mirar si hay una mosca
   Here si means if / whether and introduces an indirect yes/no question: to see whether there is a fly.

So the sentence has:

• one if for a condition
• one if/whether for checking something

This is very common in Spanish.

Ir a + infinitive is a very common way to talk about the future in Spanish, especially in everyday speech.

• va a mirar = is going to look / is going to check
• mirará = will look

Both are possible, but va a mirar often sounds a bit more natural and conversational.

In this sentence, mi hija va a mirar suggests a simple expected action in the future: she’s going to check.

Here mirar does not just mean to look at. It can also mean to check or to look to see.

So:

• mirar si hay una mosca = to check whether there is a fly
• more naturally in English: to look and see if there is a fly

A close alternative would be:

• va a ver si hay una mosca

Both are natural, though mirar is very common in Spain.

Hay is used to say that something exists or is present somewhere:

• hay una mosca = there is a fly

You use hay with indefinite things like:

• una mosca
• un perro
• unas casas

By contrast:

• está is used for the location of a specific thing
  
  • La mosca está sobre el agua = The fly is on the water
• es is used for identity or description, not existence

So si hay una mosca means if there is a fly, not if the fly is.

Because the sentence is talking about any fly, not a specific one already known to the listener.

• una mosca = a fly
• la mosca = the fly

Since the speaker is saying the daughter will check whether there is a fly, the fly has not been identified yet, so the indefinite article una is the natural choice.

This is a very common question.

Agua is grammatically feminine, but in the singular it normally uses el instead of la because it begins with a stressed a- sound. This avoids the awkward sound of la agua.

So:

• el agua
• el águila
• el alma

But the noun is still feminine, which you can see in other words around it:

• el agua fría = cold water
  (fría, not frío)
• las aguas = the waters

So in your sentence, sobre el agua is correct.

Because sobre and en give different images:

• sobre el agua = on the water / above the water / on the surface of the water
• en el agua = in the water

If the fly is floating or resting on the surface, sobre el agua makes sense. If it were submerged or simply in the water, en el agua would be more appropriate.

Spanish often leaves subject pronouns out because the verb ending usually makes the subject clear.

• encontramos already tells you we find
• va a mirar could be understood from context, but here mi hija is stated explicitly as the subject

So Spanish prefers:

• Si encontramos una charca, mi hija va a mirar...

rather than:

• Si nosotros encontramos una charca, ella va a mirar...

The pronouns are possible, but they would usually be added only for emphasis or contrast.

No. In this sentence, si hay una mosca is correct.

After mirar si, Spanish normally uses the indicative, because the speaker is checking a factual question:

• mirar si hay = check whether there is
• preguntar si viene = ask whether he/she is coming

So:

• mirar si hay una mosca ✅
• mirar si haya una mosca ❌

The subjunctive is not used here.

Charca usually means a small body of still water, such as a pond, pool, or sometimes a large puddle, depending on context.

In Spain, it often suggests something smaller and less formal than:

• estanque = pond/tank, often man-made
• lago = lake

So una charca gives the idea of a small patch of standing water in nature.

Yes. A very natural alternative is:

• Si encontramos una charca, mi hija va a ver si hay una mosca sobre el agua.

Here ver si... means to see if... and is extremely common.

The difference is small:

• mirar si... = look/check if...
• ver si... = see if...

In many contexts, both work well.

Spanish word order is flexible, but the version given is very natural:

• Si encontramos una charca, mi hija va a mirar si hay una mosca sobre el agua.

You can move elements around, but some versions sound more marked or less natural. For example, Spanish usually likes to keep the subject and verb reasonably close together unless there is a reason to emphasize something.

So while word order can vary, the original sentence is a normal, straightforward way to say it.