Az úszómester megnézi a mélységet, hacsak az úszásoktató nem ellenőrzi.

This is one of the most common things learners notice.

In Hungarian, hacsak ... nem is a fixed pattern meaning unless. Even though nem normally means not, in this construction it does not make the clause negative in the same way English not would.

So:

• hacsak ... nem = unless
• Hacsak az úszásoktató nem ellenőrzi = unless the swimming instructor checks it

You should learn this as a set expression rather than translating each word separately.

A few similar examples:

• Elmegyek, hacsak nem esik.
  = I’ll go, unless it rains.
• Megveszem, hacsak nem túl drága.
  = I’ll buy it, unless it’s too expensive.

So the nem is required by the Hungarian structure, even though the overall meaning is not a simple negative.

Both can be translated as checks, but they are not exactly the same.

• megnézi literally means something like looks at, takes a look at, or checks by looking
• ellenőrzi means inspects, verifies, or checks more formally/systematically

So in this sentence:

• Az úszómester megnézi a mélységet
  suggests the lifeguard looks at / checks the depth
• az úszásoktató nem ellenőrzi
  suggests the instructor does not inspect / verify it

The choice of these two verbs may reflect a slight nuance:

• megnézi = more everyday, practical checking
• ellenőrzi = more deliberate or official checking

Because mélységet is the accusative form, and it marks the direct object of the verb.

• mélység = depth
• mélységet = depth as the thing being checked

In Hungarian, direct objects usually take -t:

• könyv → könyvet
• vizsga → vizsgát
• mélység → mélységet

So:

• megnézi a mélységet = checks the depth

Without the accusative ending, the noun would not be marked as the direct object.

Hungarian often uses the definite article where English might or might not use one.

Here:

• a mélységet = the depth

This sounds natural in Hungarian because it refers to the specific depth of the water in that situation, not just the abstract concept of depth.

Hungarian articles:

• a before consonant sounds
• az before vowel sounds

So:

• a mélységet
• az úszómester
• az úszásoktató

Even when English might say checks depth in a more general or technical style, Hungarian usually prefers a mélységet in a normal sentence like this.

Because both nouns begin with a vowel sound.

Hungarian definite articles have two forms:

• a before consonants
• az before vowels

So:

• az úszómester
• az úszásoktató
• but a mélység

This is similar to English a/an, but Hungarian uses this difference only for the definite article, not the indefinite one.

Those are third person singular definite-conjugation verb forms.

Hungarian verbs change depending not only on the subject, but also on whether the object is definite.

Here the object is definite:

• a mélységet = the depth

So Hungarian uses the definite conjugation:

• megnézi = he/she checks it / looks at it
• ellenőrzi = he/she checks/inspects it

Compare:

• megnéz egy filmet = he watches a film
  (indefinite object)
• megnézi a filmet = he watches the film
  (definite object)

In your sentence, the verbs are in definite conjugation because the object is understood as definite.

Because Hungarian often leaves out an object if it is clear from context.

The first clause already mentions:

• a mélységet = the depth

So in the second clause, Hungarian does not need to repeat it:

• hacsak az úszásoktató nem ellenőrzi = unless the swimming instructor checks it

The it is understood from the previous clause.

This is very common in Hungarian. If the object is obvious, it can be omitted.

The prefix meg- often gives a sense of completion, result, or a single completed action.

Compare:

• nézi = is looking at / watches
• megnézi = looks at, checks, watches through, has a look at

So megnézi a mélységet feels more like:

• checks the depth
• takes a look at the depth
• has a look to see what the depth is

Without meg-, the verb could sound more ongoing or less goal-oriented, depending on context.

Verb prefixes are very important in Hungarian, and meg- is one of the most common ones.

Yes, Hungarian word order is flexible, but different orders change the focus or emphasis.

The version here is a neutral, natural order:

• Az úszómester megnézi a mélységet.

This presents the subject first, then the verb, then the object.

Other orders are possible, for example:

• A mélységet az úszómester nézi meg.
  This puts more focus on the depth.
• Az úszómester a mélységet nézi meg.
  This can emphasize what exactly the lifeguard checks.

So the given order is a straightforward neutral sentence, which is usually the best kind for learners to start with.

Often yes in many contexts, but not always perfectly.

• úszómester literally means something like swimming master
• In practice, it often refers to a lifeguard or pool staff member responsible for swimmer safety

Meanwhile:

• úszásoktató = swimming instructor

So the contrast in the sentence is between:

• the person supervising the pool / water safety
• the person teaching swimming

Depending on the exact setting, úszómester might carry a slightly different nuance from English lifeguard, but lifeguard is usually the most natural translation.

Not exactly. That would change the logic.

The Hungarian sentence uses hacsak ... nem, which means unless.

So the meaning is:

• The lifeguard checks the depth, unless the swimming instructor checks it.

That implies:

• normally the lifeguard does it
• but if the instructor does it, then the lifeguard does not need to

If you translated it as:

• if the swimming instructor doesn’t check it

that would mean almost the opposite condition.

So this is a good example of why hacsak ... nem has to be learned as a unit meaning unless.

In Hungarian, nem usually comes directly before the element it negates, and in simple clauses it typically comes before the verb.

So:

• nem ellenőrzi = does not check / does not inspect

In this sentence, even though the whole expression hacsak ... nem means unless, the placement of nem still follows normal Hungarian syntax: it comes before the verb.

This is the standard pattern:

• nem látja = doesn’t see it
• nem tudja = doesn’t know it
• nem ellenőrzi = doesn’t check it

Inside the hacsak ... nem construction, that same word order remains.