Gjenutsettingen skjer i ferskvannet.

Because Norwegian usually puts the definite article at the end of the noun instead of using a separate word like the.

So:

• gjenutsetting = a re-release / reintroduction
• gjenutsettingen = the re-release / the reintroduction

The ending -en is the definite ending for many non-neuter nouns in Bokmål.

It is a compound noun built from smaller parts:

• gjen- = again, re-
• utsetting = release, putting out, setting out

So gjenutsetting literally means something like re-release or reintroduction, depending on context.

This kind of long compound word is very common in Norwegian.

In Norwegian, the definite article is usually attached to the noun as a suffix.

Compare:

• en bil = a car
• bilen = the car

In this sentence:

• gjenutsettingen = the re-release
• ferskvannet = the freshwater

So English uses a separate word, but Norwegian often uses an ending instead.

Skjer is the present tense of å skje, which means to happen or to take place.

So Gjenutsettingen skjer ... means that the event happens or takes place somewhere.

This is more natural than using er here, because the sentence is describing an event occurring, not simply identifying something.

Yes, it is somewhat irregular and very common, so it is worth memorizing.

The infinitive is:

• å skje = to happen

The present tense is:

• skjer = happens

So you cannot form it by just adding a regular ending to get something like skjeer. The correct form is simply skjer.

I is the preposition meaning in.

So:

• i ferskvann = in freshwater
• i ferskvannet = in the freshwater

The definite form ferskvannet can suggest a specific freshwater environment already understood from the context.

In some contexts, i ferskvann would also be possible if you mean freshwater more generally.

Because ferskvann is a neuter noun.

For many neuter nouns in Bokmål:

• indefinite: et ferskvann or more commonly just ferskvann in many contexts
• definite: ferskvannet

So:

• -en often appears with masculine/common-gender nouns
• -et often appears with neuter nouns

That is why you get gjenutsettingen but ferskvannet.

Yes. Norwegian very often writes compound nouns as one word.

So:

• fersk = fresh
• vann = water
• ferskvann = freshwater

English sometimes separates or hyphenates expressions where Norwegian prefers a single compound word.

The sentence follows normal Norwegian main-clause word order:

• Gjenutsettingen = subject
• skjer = verb
• i ferskvannet = prepositional phrase showing location

So the pattern is:

• subject + verb + adverbial/location

This is very typical Norwegian word order in a simple statement.

Yes, it could, but then Norwegian keeps the verb in second position.

For example:

• I ferskvannet skjer gjenutsettingen.

That is grammatical, but it changes the emphasis so that the location comes first.

This shows an important Norwegian rule: in main clauses, the finite verb usually stays in second position.