Ako ne bude kiše, ići ćemo pješice uz rijeku.

In standard Croatian, future situations inside an ako clause are usually expressed without će. So you say:

Ako ne bude kiše, ići ćemo...

rather than:

Ako neće biti kiše...

This is actually similar to English, where we say If it doesn’t rain, we’ll go, not usually If it won’t rain, we’ll go.

So for a learner, the safest pattern is:

• ako
  • bude / present form
• main clause + future

That is why the sentence uses Ako ne bude kiše, ići ćemo...

Formally, bude is a present-tense form from the budem set of forms of biti. But in sentences like this, it refers to the future because the whole ako clause is about a future possibility.

So:

• Ako ne bude kiše... = a future condition
• bude looks like present tense
• but its meaning here is future-oriented

This is a very common Croatian pattern after words like ako, kad, čim, and similar conjunctions.

Because kiše is the genitive singular of kiša, and Croatian often uses the genitive in expressions meaning there is / there isn’t / there will be with an indefinite amount of something.

So:

• kiša = nominative singular
• kiše = genitive singular

In this sentence, ne bude kiše means something like there will be no rain or there won’t be any rain.

This is a very common pattern, especially with:

• weather words
• mass nouns
• negation

Compare:

• ima vode = there is water
• nema vremena = there is no time
• bit će snijega = there will be snow
• ne bude kiše = there won’t be rain

You may hear forms like that in everyday speech, but for standard Croatian and for learning good grammar, Ako ne bude kiše is the better choice.

So:

• Ako ne bude kiše = standard and recommended
• Ako neće biti kiše = less standard in this kind of conditional sentence

If you are unsure, use Ako ne bude...

Croatian future tense is made with the infinitive plus a short auxiliary form such as ću, ćeš, će, ćemo.

Here the verb is ići and the auxiliary is ćemo:

• ići ćemo = we will go

The short auxiliary normally cannot stand at the very beginning of its clause. Since the main clause starts with the verb, Croatian puts the infinitive first:

ići ćemo

If another word comes first, then the auxiliary can follow that first word:

• Sutra ćemo ići...
• Mi ćemo ići...

So in this sentence, ići ćemo is exactly what you expect.

Pješice is an adverb, and it means on foot.

So:

• ići pješice = to go on foot
• doći pješice = to arrive on foot

It does not change for gender, number, or case here. It is just a fixed adverb used with verbs of movement.

Rijeku is the accusative singular of rijeka.

The preposition uz takes the accusative, so:

• rijeka = nominative
• rijeku = accusative

That is why the sentence says:

uz rijeku

not uz rijeka or uz rijeci.

Here uz rijeku most naturally means along the river.

It suggests movement following the river, probably along the riverbank or beside it.

So the phrase gives the idea of direction/path, not just location. If you only wanted to say by the river in a more static sense, Croatian might also use expressions like kraj rijeke or pokraj rijeke.

In this sentence, though, uz rijeku fits well because the action is walking.

Yes. In standard Croatian, a subordinate clause introduced by ako is separated by a comma.

So:

Ako ne bude kiše, ići ćemo pješice uz rijeku.

If the ako clause comes first, the comma goes after it. This is standard punctuation.

Yes. Croatian word order is fairly flexible, so you could also say:

Ići ćemo pješice uz rijeku ako ne bude kiše.

The basic meaning stays the same.

The difference is mostly about emphasis:

• Ako ne bude kiše, ići ćemo... puts the condition first
• Ići ćemo... ako ne bude kiše. states the plan first, then adds the condition

Even when word order changes, the clitic rules still matter, so forms like ćemo still need to be in a natural clitic position.