Encima del banco había una paloma, y más lejos vimos una gaviota sobre el agua.

Because Spanish normally uses haber to say that something exists or is present somewhere.

• Había una paloma = There was a pigeon
• Estaba una paloma is not the normal way to introduce a new thing in a scene

If you use estar, you usually mean the thing is already identified:

• La paloma estaba encima del banco = The pigeon was on the bench

So:

• haber = existence / there was, there were
• estar = location or state of something specific

They are similar, but not always identical.

• encima de usually means on top of or above
• sobre can mean on, over, or above, and is a bit broader

In this sentence:

• Encima del banco suggests the pigeon was on top of the bench
• Sobre el agua suggests the gull was over the water

In many contexts they can overlap, but these choices sound very natural.

Because de + el contracts to del.

So:

• de + el = del
• a + el = al

Examples:

• encima del banco
• al lado del banco
• voy al banco

This contraction is normally required.

Because both nouns are feminine:

• la paloma
• la gaviota

So in the singular indefinite form, they take una:

• una paloma
• una gaviota

This is just grammatical gender. It does not necessarily tell you the biological sex of the bird.

This is a very common Spanish pattern.

Agua is grammatically feminine, but in the singular it uses el because it begins with a stressed a- sound. Spanish does this to avoid the awkward sequence la agua.

So you get:

• el agua
• el águila
• el arma

But the noun is still feminine, which you can see in adjectives:

• el agua fría
• el águila blanca

And in the plural, it goes back to las:

• las aguas

It means farther away or further away.

• lejos = far
• más lejos = farther / further away

In the sentence, it tells you that the gull was seen at a greater distance than the pigeon.

Because vimos is the preterite, which is used for a completed event:

• vimos una gaviota = we saw a gull

It presents the sighting as a single event in the story.

If you said veíamos, that would be the imperfect, which usually gives background, ongoing action, or repeated action:

• Veíamos una gaviota sobre el agua = We could see / were seeing a gull over the water

So vimos fits better if the idea is then we spotted a gull.

Because Spanish often leaves subject pronouns out when the verb already makes the subject clear.

• vimos already means we saw

So nosotros is unnecessary unless you want emphasis or contrast:

• Nosotros vimos una gaviota, pero ellos no = We saw a gull, but they didn’t

This omission of subject pronouns is very normal in Spanish.

Because Spanish word order is flexible, especially in descriptive sentences.

Both are possible:

• Encima del banco había una paloma
• Había una paloma encima del banco

Starting with Encima del banco puts the location first, which helps set the scene. It feels a bit like: On top of the bench, there was a pigeon.

So the writer is focusing first on where.

Again, this is because Spanish allows fairly flexible word order.

• y más lejos vimos una gaviota
• y vimos una gaviota más lejos

Both are possible, but the first version highlights the idea of distance earlier.

Placing más lejos before the verb gives it a little more prominence: first the sentence tells you where, then it tells you what we saw.

The accent mark shows the correct stress and pronunciation:

• ha-bí-a

Without the accent, you might not know how to divide or stress the vowels properly. In forms like había, tenía, comía, the accent helps show that -ía is pronounced clearly.

So había has three syllables, not two.

Yes. In this existential use, había is often translated as either there was or there were, depending on what follows.

• Había una paloma = There was a pigeon
• Había dos palomas = There were two pigeons

So the English translation changes, but Spanish still uses había.