Il y a trop de moustiques près du lac le soir, alors nous restons au bord de la mer.

Il y a is the standard French expression for there is / there are.

In this sentence, Il y a trop de moustiques means There are too many mosquitoes.

Literally, il y a comes from something like it has there, but you should learn it as a fixed expression meaning there is / there are.

Examples:

• Il y a un lac. = There is a lake.
• Il y a des moustiques. = There are mosquitoes.

After expressions of quantity like trop de, French uses de, not des.

So:

• trop de moustiques = too many mosquitoes
• beaucoup de moustiques = a lot of mosquitoes
• peu de moustiques = few mosquitoes

Even though moustiques is plural, the article changes to de after a quantity expression.

Compare:

• des moustiques = some mosquitoes
• trop de moustiques = too many mosquitoes

Près de means near.

So:

• près de + le lac becomes près du lac

This happens because de + le = du in French.

Examples:

• près du lac = near the lake
• près du parc = near the park
• près de la mer = near the sea
• près de l’hôtel = near the hotel

So du here is just the contraction of de le.

In French, le soir often means in the evening / in the evenings / at night, depending on context.

In this sentence, près du lac le soir means near the lake in the evening or at night near the lake.

French often uses le + time expression where English uses a preposition:

• le matin = in the morning
• l’après-midi = in the afternoon
• le soir = in the evening

So le soir is the normal idiomatic way to say this.

Here, alors means so, therefore, or as a result.

It links the two ideas:

• there are too many mosquitoes near the lake in the evening,
• so we stay by the sea.

It is a very common connector in French.

Examples:

• Il pleut, alors je reste à la maison. = It’s raining, so I’m staying home.
• Je suis fatigué, alors je me couche tôt. = I’m tired, so I’m going to bed early.

The verb rester means to stay / remain.

In this sentence, rester au bord de la mer means to stay by the seaside / by the sea. You do not need à before au bord de la mer because au bord de is already a complete location expression.

So:

• nous restons = we stay
• au bord de la mer = by the sea / at the seaside

Together:

• nous restons au bord de la mer = we stay by the sea

Yes. The French present tense often covers both:

• we stay
• we are staying
• sometimes even we do stay, depending on context

So nous restons can mean:

• we stay
• we’re staying

French does not always distinguish between simple present and present progressive the way English does.

If French specifically wants to emphasize are staying / are in the process of staying, it can use être en train de, but that is not necessary here.

Good question. They are similar, but not exactly the same.

• près de la mer = near the sea
• au bord de la mer = at the edge of the sea / by the seaside / on the shore

Au bord de suggests being right next to the water or on the coastline.
Près de is a bit more general and could mean nearby, not necessarily right on the edge.

So in this sentence, au bord de la mer gives a stronger image of being by the coast.

Because sur la mer means on the sea, as if you are physically on top of it, for example in a boat.

But au bord de la mer means by the sea, on the shore or coast.

Compare:

• Nous sommes au bord de la mer. = We are by the sea.
• Nous sommes sur la mer. = We are on the sea.

So au bord de la mer is the correct choice for being on land next to the water.

This is because of the gender of the nouns and the way de combines with the article.

• le lac is masculine singular
  → de + le = du
  → près du lac

• la mer is feminine singular
  → de + la = de la
  → au bord de la mer

So:

• du = de + le
• de la stays de la
• de l’ is used before a vowel sound

Examples:

• près du parc
• près de la plage
• près de l’océan

In this sentence, moustiques means mosquitoes.

French moustique is the normal word for a mosquito. It does not usually mean gnat. If the meaning shown to the learner is mosquitoes, that is the correct interpretation here.

It is not always strictly required, but it is very natural here.

The comma helps separate:

1. the reason: Il y a trop de moustiques près du lac le soir
2. the result: alors nous restons au bord de la mer

So the punctuation matches the logic of the sentence: There are too many mosquitoes..., so we stay by the sea.

French punctuation is sometimes a little more flexible than English, but this comma is perfectly normal.

Yes, very often in everyday spoken French, people would say on instead of nous.

So you might hear:

• ... alors on reste au bord de la mer.

That means the same thing as:

• ... alors nous restons au bord de la mer.

Difference:

• nous restons sounds a bit more formal or written
• on reste sounds more natural in casual spoken French

Both are correct.

It can depend on context, but here it most naturally sounds like a general habit or repeated situation: in the evening / evenings.

So the idea is something like: There are too many mosquitoes near the lake in the evening, so we stay by the sea.

If you wanted to make it clearly one specific evening, French would usually add more context, such as:

• ce soir = tonight / this evening

Compare:

• le soir = in the evening / in the evenings
• ce soir = this evening / tonight

So here le soir is probably general rather than one single evening.