Anates in lacu natant, quia aqua ibi quieta est.

Because anates is in the nominative plural, which is the case normally used for the subject.

The dictionary form is anas, anatis, meaning duck. Its nominative plural is anates, so anates natant means the ducks swim or ducks are swimming.

Also, natant is a plural verb form, so it matches a plural subject.

Natant is the 3rd person plural present active indicative of natare, meaning to swim.

So it means:

• they swim
• they are swimming

Latin present tense often covers both the simple present and the progressive present in English.

Because in can take two different cases depending on the meaning:

• in + ablative = in / on a place, showing location
• in + accusative = into / onto a place, showing motion toward

Here the ducks are already swimming in the lake, so this is location, not movement into the lake. That is why Latin uses the ablative: in lacu.

If the sentence meant The ducks swim into the lake, Latin would use in lacum.

Lacu is ablative singular of lacus, meaning lake.

So in in lacu, the noun is in the ablative because in is expressing location.

You may also see it written with a macron as lacū. The macron marks a long vowel, but many Latin texts leave macrons out.

Quia means because. It introduces the reason:

• Anates in lacu natant = the ducks swim in the lake
• quia aqua ibi quieta est = because the water there is calm

So the second clause explains why the ducks are swimming there.

Because aqua is the subject of est in the clause quia aqua ibi quieta est.

In that clause:

• aqua = the subject, water
• est = is
• quieta = an adjective describing aqua

So aqua must be nominative singular.

Because it agrees with aqua.

In Latin, adjectives agree with the nouns they describe in:

• gender
• number
• case

Since aqua is feminine singular nominative, quieta must also be feminine singular nominative.

So aqua quieta est means the water is calm or the water is still.

Not in the modern English sense of not making noise. With water, quieta means something more like:

• calm
• still
• undisturbed

So aqua quieta est is best understood as the water is calm.

Ibi means there.

It adds the idea that the water is calm there, in that place. So:

• aqua ibi quieta est = the water there is calm

Latin often uses adverbs like ibi to make location clearer, even when the place has already been mentioned.

Latin word order is much more flexible than English word order because Latin uses endings to show grammatical function.

English depends heavily on word order:

• The ducks swim in the lake because the water there is calm

Latin can move words around more freely:

• Anates in lacu natant, quia aqua ibi quieta est
• In lacu anates natant, quia ibi aqua quieta est
• and other variations

The basic meaning stays the same because the endings show what each word is doing. Word order in Latin often changes for emphasis, style, or rhythm rather than grammar alone.

Classical Latin does not have articles like English the and a/an.

So anates can mean:

• ducks
• the ducks

And aqua can mean:

• water
• the water

You decide which English translation sounds right from the context.

Yes. Latin present tense often covers both meanings.

So anates natant can be translated as:

• the ducks swim
• the ducks are swimming

English chooses between those two based on context and style, but Latin does not need a separate form here.

The comma is just punctuation added by an editor or textbook writer to make the sentence easier to read.

Latin manuscripts originally had much less punctuation than modern printed texts. The grammar does not depend on the comma. It simply helps show that quia aqua ibi quieta est is the explanatory clause.

Yes, in fully marked Latin you might see macrons, such as:

• lacū instead of lacu

Macrons show vowel length, which matters for pronunciation and sometimes for poetry and grammar study. But many beginner texts and many printed Latin texts leave them out.

So lacu and lacū are the same word; the second spelling just gives you more pronunciation information.