Poslije kiše potok je bio bistar i miran.

Because poslije normally takes the genitive case.

• Base noun: kiša = rain
• Genitive singular: kiše

So poslije kiše means after the rain / after rain.

This is a very common pattern in Croatian:

• poslije ručka = after lunch
• poslije škole = after school
• poslije posla = after work

A learner should remember poslije + genitive.

Yes. Poslije and nakon can both mean after in this kind of sentence.

• poslije kiše
• nakon kiše

Both are natural. In many contexts, they are interchangeable. A learner will hear both in real Croatian. Poslije may feel a bit more everyday in some situations, but both are standard and correct.

Because Croatian usually needs the auxiliary verb je in the past tense.

The past tense here is formed like this:

• je = auxiliary (is/has-type helper verb, from biti = to be)
• bio = past active participle

Together:

• je bio = was

So:

• potok je bio = the stream was

You normally cannot leave out je in standard Croatian prose here.

Bio is the masculine singular past participle of biti (to be).

It agrees with potok, which is:

• masculine
• singular

So the form must also be masculine singular:

• masculine singular: bio
• feminine singular: bila
• neuter singular: bilo

For example:

• Rijeka je bila mirna. = The river was calm.
• Jezero je bilo mirno. = The lake was calm.

Since potok is masculine, bio is the correct form.

They agree with potok in gender, number, and case.

Potok is:

• masculine
• singular
• nominative (it is the subject)

So the adjectives must also be masculine singular nominative:

• bistar
• miran

If the noun changed, the adjectives would change too. For example:

• rijeka je bila bistra i mirna
• jezero je bilo bistro i mirno

This is a very important feature of Croatian grammar: adjectives must match the noun they describe.

Because Croatian has no articles like English a/an/the.

So potok can mean:

• a stream
• the stream

The exact meaning depends on context.

This is normal in Croatian. Learners coming from English often expect an article, but Croatian simply does not use one.

Yes, Croatian word order is fairly flexible.

The sentence begins with Poslije kiše to set the time/background first: after the rain.

That is very natural. But other orders are also possible, for example:

• Potok je bio bistar i miran poslije kiše.
• Bistar i miran potok je bio poslije kiše. (more marked/literary)

The most neutral version here is probably the given one, because it starts with the circumstance and then gives the main statement.

Croatian often moves parts of the sentence around for emphasis, rhythm, or style.

This relates to a very common Croatian rule: certain short unstressed words, called clitics, tend to come in the second position of the clause.

Here, je is a clitic.

In:

• Poslije kiše potok je bio bistar i miran.

the clitic je appears after the first phrase of the main clause structure. Learners will often notice that these little words do not always stand where English speakers expect them.

Compare:

• Potok je bio miran.
• Jučer je bio miran.
• Poslije kiše je bio miran.
• Poslije kiše potok je bio miran.

Clitic placement is a big topic in Croatian, but for now it is enough to recognize that je is an unstressed helper word that usually cannot stand freely anywhere.

Here bistar means something like:

• clear
• transparent
• not muddy

When used about water, a stream, or a liquid, bistar refers to physical clarity.

Be careful: bistar can also describe a person’s mind, meaning bright, sharp, or quick-witted. So the word has more than one use, depending on context.

In this sentence, because the subject is potok, the meaning is clearly the water-related one.

Here miran means:

• calm
• still
• peaceful

For a stream, it suggests the water was not rough, violent, or disturbed.

Like many Croatian adjectives, miran can be used in different contexts:

• a miran čovjek = a calm/peaceful person
• a mirno more = a calm sea
• a miran dan = a peaceful day

So in this sentence it describes the stream as calm and gentle.

Usually, yes. In Croatian, nouns ending in a consonant are very often masculine.

So potok is masculine, and that affects:

• the past tense form: bio
• the adjectives: bistar, miran

This is a helpful pattern, though not every noun can be guessed perfectly just from the ending. But for potok, masculine is exactly right.

Sometimes yes, but not in exactly the same way as in this full sentence.

Croatian often drops subject pronouns like he/she/it, because the verb form already gives information. But here potok is a full noun, not a pronoun. If the noun had already been mentioned, a speaker might choose a shorter sentence in context, but the full version with potok is completely natural and clear.

For example, after already talking about the stream, someone might say:

• Poslije kiše bio je bistar i miran.

That can work in context. But if you want the sentence to stand alone clearly, keeping potok is better.

The verb participle and adjectives would change to match the feminine noun.

With rijeka:

• Poslije kiše rijeka je bila bistra i mirna.

Changes:

• bio → bila
• bistar → bistra
• miran → mirna

This is a very useful comparison because it shows agreement clearly. Croatian constantly changes adjective and past forms to match the noun.