Learn Hardcore French: En été, nous allons à la piscine pour faire de la natation quand il fait très chaud. - In summer, we go to the pool to swim when it is very hot.

You can also say L’été, nous allons… (literally “Summer, we go…”) to mean “In (the) summer, we go…”, but when you use a preposition, it’s en été, not anything else.

Is the comma after En été required?

In French, a comma is very often used after an introductory time expression like En été. It separates that time phrase from the main clause:

En été, nous allons…

Is it absolutely grammatically mandatory? Not always, but it’s:

very common
considered good style
helpful for clarity

So you should generally keep it: a short time phrase at the beginning of the sentence is normally followed by a comma.

What exactly does nous allons mean here: “we go”, “we are going”, or “we will go”?

French nous allons is in the present tense of aller (to go), and it can cover several English meanings depending on context:

Habitual action:
- En été, nous allons à la piscine…
  → “In summer, we go to the pool…”
Right-now or general present:
- Nous allons à la piscine maintenant.
  → “We are going to the pool (now).”

French present tense does not distinguish strictly between we go and we are going the way English does. Context decides which translation is best.

To talk about the near future, French also uses aller + infinitive:

Nous allons aller à la piscine. – “We are going to go to the pool.”
But in your sentence, it’s simply a present tense describing a regular summer habit.

Why is it à la piscine and not au piscine?

French contracts à + le → au, but it does not contract à + la.

le (masculine singular) → au
- à + le parc → au parc
la (feminine singular) → à la (no change)
- à + la piscine → à la piscine
les (plural) → aux
- à + les magasins → aux magasins

Since piscine is feminine (la piscine), you say à la piscine, not au piscine.

Why is it à la piscine (“to the pool”) and not dans la piscine (“in the pool”)?

à la piscine means “to the pool / at the pool” – you’re talking about the place as a destination or location:
- Nous allons à la piscine. – We go to the pool.
dans la piscine means “in the pool” – you’re talking about being inside the water:
- Les enfants sont dans la piscine. – The children are in the pool.

In your sentence, the focus is on going to that facility (the swimming pool), not physically being in the water at that moment, so à la piscine is correct.

Why do we use la piscine and not just say nous allons à piscine without an article?

In French, you almost always need an article (le, la, les, un, une, des) before a common noun like piscine.

English can say “to school”, “to church”, but French normally requires:

à la piscine – to the pool
à l’école – to school
à l’église – to church

Leaving out the article (“à piscine”) is incorrect in standard French.

Here, la piscine is “the swimming pool” in a general sense (the pool we usually go to / the local pool), and French uses the definite article la for that.

Why is it pour faire de la natation and not just pour nager?

Both are possible, but they have slightly different nuances:

pour nager – “in order to swim”
→ Focus on the action of swimming itself.
pour faire de la natation – “in order to do swimming / to go swimming (as an activity/sport)”
→ Emphasizes swimming as a sport or regular activity.

In many everyday contexts, pour nager and pour faire de la natation can be used interchangeably.

Your sentence with faire de la natation suggests swimming as a regular activity or sport you do when it’s hot, not just for a random quick swim.

Why is it de la natation and not la natation or du natation?

Natation (swimming) is a feminine noun in French: la natation.

When you say faire de + (sport / activity), you normally use the partitive article (du / de la / de l’ / des):

faire du tennis – to play tennis
faire de la musique – to make / play music
faire de la natation – to do swimming
faire de l’athlétisme – to do athletics
faire des mathématiques – to do mathematics

So:

de la natation (correct):
- de la = de + la (for a feminine noun)

You cannot say:

du natation – wrong, because natation is feminine (should be de la)
faire la natation – wrong pattern; faire with activities usually needs the partitive de la, not a simple definite article.

So faire de la natation is the standard structure.

Why do we say quand il fait très chaud and not quand c’est très chaud?

For weather in French, there are special expressions. To say it is hot (weather), you use il fait chaud, not c’est chaud:

Il fait chaud. – It’s hot (the weather is hot).
Il fait très chaud. – It’s very hot.

C’est chaud can mean “that’s hot” in other contexts (touching something, figurative uses, slang), but for the weather, the normal verbs are:

il fait (with an adjective or noun):
- il fait chaud, il fait froid, il fait beau, il fait mauvais, il fait du vent…
sometimes il y a (with a noun):
- il y a du vent, il y a du soleil, il y a du brouillard…

So in your sentence, quand il fait très chaud is the correct weather expression.

What does the il refer to in il fait très chaud? Is there a subject?

The il in il fait très chaud is an impersonal pronoun.

It does not refer to a person or thing like “he”, “it”, etc.
It’s just a grammatical subject used because French sentences need an explicit subject, even when English just says “it is…” in a non-specific way.

Other common impersonal expressions:

Il pleut. – It’s raining.
Il neige. – It’s snowing.
Il fait froid. – It’s cold.
Il est tard. – It’s late.

So il here just fills the subject position; it doesn’t refer to a specific object or person.

Could we move parts around, like say Nous allons à la piscine en été quand il fait très chaud? Is the word order flexible?

Yes, the word order is somewhat flexible in French, especially for time expressions. These are all grammatically correct, with slightly different emphasis:

En été, nous allons à la piscine quand il fait très chaud.
→ Emphasis on En été (in summer).
Nous allons à la piscine en été quand il fait très chaud.
→ More neutral, everything after the verb.
Nous allons à la piscine quand il fait très chaud, en été.
→ Emphasis at the end on en été (less common, but possible).

French often puts short time expressions at the beginning for emphasis or clarity, and separates them with a comma. But placing en été after the verb is also fine. The important fixed parts are:

aller à la piscine
faire de la natation
il fait très chaud

Those expressions themselves don’t change internal order.

Could I replace quand with lorsque in quand il fait très chaud?

Yes, you can:

En été, nous allons à la piscine pour faire de la natation lorsqu’il fait très chaud.

Quand and lorsque are very close in meaning (“when”). Differences:

Quand is more common and neutral in speech and writing.
Lorsque is often a bit more formal or literary, more frequent in written French.

In everyday conversation, quand is more natural, but both are correct here.