Der er mange myg ved vandet i aften.

Der er is the standard Danish way to say there is / there are when you are talking about the existence of something.

So in Der er mange myg ..., der er means there are.

This is called an existential construction:

• Der er en bog på bordet. = There is a book on the table.
• Der er mange mennesker her. = There are many people here.

Even though der often means there in a location sense, here it does not mean a physical place. It is just part of the pattern der er.

Because Danish uses der in existential sentences, where English uses there:

• Der er mange myg. = There are many mosquitoes.

By contrast, det usually means it or that:

• Det er en myg. = It is a mosquito.
• Det er irriterende. = It is annoying.

So:

• der er = there is/are
• det er = it is

A learner can think of der er as a fixed expression.

Use mange with countable plural nouns, and meget with uncountable nouns or amounts.

Here, myg means mosquitoes, and mosquitoes are countable, so Danish uses mange:

• mange myg = many mosquitoes

Compare:

• mange bøger = many books
• mange mennesker = many people
• meget vand = much water
• meget tid = much time

So mange myg is correct because you can count mosquitoes.

Because some Danish nouns have the same form in singular and plural indefinite.

So:

• en myg = a mosquito
• mange myg = many mosquitoes

This is normal in Danish. Not all nouns change in the plural.

For comparison:

• en bil → biler
• en bog → bøger
• en myg → myg

You usually understand whether it is singular or plural from the article or other words around it:

• en myg = singular
• to myg, mange myg = plural

Ved usually means by, near, next to, at depending on context.

So ved vandet means something like:

• by the water
• near the water
• down by the water

It does not necessarily mean literally touching the water. It just means in that area.

Examples:

• ved huset = by the house
• ved stranden = by the beach
• ved bordet = at the table

In this sentence, ved vandet suggests that the mosquitoes are around the waterside area.

Because vandet is the definite form of vand.

• vand = water
• vandet = the water

Danish often puts the definite article at the end of the noun instead of using a separate word like English the.

So:

• en bog = a book
• bogen = the book

For neuter nouns like vand:

• et hus = a house
• huset = the house
• vand / vandet = water / the water

In this sentence, ved vandet is most naturally by the water, meaning a specific body of water or waterside area already understood from context.

Because Danish normally adds definiteness as a suffix to the noun.

English:

• the water

Danish:

• vandet

This is one of the biggest structural differences from English.

A few more examples:

• the car = bilen
• the child = barnet
• the mosquitoes = myggene

So the idea of the is already built into vandet.

I aften means this evening / tonight.

It is a common time expression in Danish:

• i dag = today
• i morgen = tomorrow
• i aften = this evening / tonight

The preposition i is simply part of the standard expression here. You do not translate it word-for-word as in every time.

So:

• i aften = tonight / this evening

In everyday Danish, this is the normal way to talk about something happening this evening.

The sentence follows a very common Danish pattern:

Der er + noun phrase + place + time

So here:

• Der er = there are
• mange myg = many mosquitoes
• ved vandet = by the water
• i aften = tonight / this evening

This word order is very natural in a neutral statement.

Danish is fairly flexible with time and place phrases, so you could also say:

• I aften er der mange myg ved vandet.
• Ved vandet er der mange myg i aften.

These versions shift the emphasis a bit, but the original sentence is perfectly normal.

Yes, absolutely.

That version is also correct:

• I aften er der mange myg ved vandet.

When a time expression like i aften comes first, Danish usually puts the verb in second position:

• I aften
  • er
    • der mange myg ved vandet

This is a very important Danish word-order rule, often called V2 word order.

Compare:

• Der er mange myg ved vandet i aften.
• I aften er der mange myg ved vandet.

Both are correct. The second one emphasizes tonight a little more.

A rough pronunciation guide is:

Der er mange myg ved vandet i aften
≈ dair air MANG-uh mewg vel VAN-neth ee OF-dn

A few notes:

• der er is often said quite quickly in normal speech.
• mange has two syllables: MANG-e
• myg has a vowel sound that does not exist in English; it is similar to a rounded front vowel.
• vandet often sounds softer than the spelling may suggest.
• aften is often pronounced something like afdn in everyday speech.

If you are learning pronunciation, it is best to listen to native audio, because Danish spelling and pronunciation often differ quite a lot.

Yes, myg is a common everyday word, especially in summer contexts.

The singular is:

• en myg = a mosquito

So it is a common gender noun (en-word).

Useful forms:

• en myg = a mosquito
• myggen = the mosquito
• myg = mosquitoes
• myggene = the mosquitoes

That makes the sentence easier to analyze:

• mange myg = many mosquitoes

In this kind of sentence, it can suggest both the literal water and the general area around it.

So ved vandet is often understood as:

• by the water
• down by the water
• near the lake/sea/river

In natural English, you might translate the whole phrase more freely as by the water rather than focusing too literally on the water itself.

That is why the sentence feels natural for a situation where mosquitoes gather near lakes, rivers, or the sea.