Learn Spanish (Latin America): Al sacar el atún del agua, lo miramos. - Upon taking the tuna out of the water, we looked at it.

The structure al + infinitive is a very common way to say "upon doing [something]" or "when doing [something]". Here, al + sacar (to take out) creates a time clause meaning "upon taking out". It is a handy shortcut that avoids conjugating a verb with cuando.

How do we know who is taking the tuna out of the water if sacar is not conjugated?

When you use al + infinitive, the subject of that action is assumed to be the same as the subject of the main clause unless specified otherwise. Since the main verb is miramos (we looked), it is naturally understood that we are the ones doing the taking.

Wait, why is it del agua? I thought agua was a feminine word.

You are right, agua is feminine! But because it starts with a stressed "a" sound, Spanish uses the masculine article el in the singular to avoid the awkward double "a" sound (la agua). Since it uses el, the preposition de combines with it to form del. If it were plural, it would go back to feminine: las aguas.

Why is it just lo miramos instead of adding a word for "at"?