Над рекой летит чайка, а у воды на камне сидит жук.

Here is the case breakdown:

• над рекой

  • рекой = instrumental singular of река
  • Reason: над usually takes the instrumental when it means above/over something.

• чайка

  • чайка = nominative singular
  • Reason: it is the subject of летит.

• у воды

  • воды = genitive singular of вода
  • Reason: у takes the genitive and means by/near.

• на камне

  • камне = prepositional singular of камень
  • Reason: на takes the prepositional when it means location, so on a rock = на камне.

• жук

  • жук = nominative singular
  • Reason: it is the subject of сидит.

So this sentence is a good example of how Russian prepositions control different cases.

This is about Russian verbs of motion.

• летит means a creature or object is flying now in a specific direction / at this moment
• летает means flies in general, flies around regularly, or is flying back and forth without focus on one directed movement

So in this sentence, Над рекой летит чайка presents a scene happening right now: a gull is flying over the river. That is why летит sounds right.

Compare:

• Чайка летит над рекой. = The gull is flying over the river right now.
• Чайка летает над рекой. = The gull flies around over the river / keeps flying over the river.

Because Russian word order is flexible and often reflects information structure, not just grammar.

In this sentence, the speaker first sets the scene:

• Над рекой = over the river
• у воды на камне = by the water, on a rock

Then the speaker tells you what is there:

• летит чайка
• сидит жук

This makes the sentence feel descriptive, almost like a picture being painted.

A more neutral order is also possible:

• Чайка летит над рекой, а жук сидит у воды на камне.

That version is grammatically correct too, but it sounds a little less like scene-setting narration.

Yes. In Russian, the subject does not have to come before the verb.

You can often identify the subject by:

• its case: usually nominative
• the verb agreement
• the overall meaning

So here:

• летит чайка = чайка is the subject
• сидит жук = жук is the subject

English relies much more heavily on word order, but Russian relies more on case endings and context.

In this sentence, а links two clauses:

• Над рекой летит чайка
• а у воды на камне сидит жук

Here а is not a strong but. It is more like:

• and
• while
• whereas
• and meanwhile

It introduces a gentle contrast or a shift of attention from one part of the scene to another.

The comma is there because Russian normally puts a comma before а when it joins two independent clauses.

So the feeling is something like:

• Over the river a gull is flying, while by the water on a rock a beetle is sitting.

These three phrases mean different things:

• у воды = by the water / near the water
• на воде = on the water
• в воде = in the water

So in your sentence:

• у воды на камне сидит жук = the beetle is near the water, sitting on a rock

It is not:

• floating on the water
• or sitting in the water

This is a very useful contrast to learn, because Russian prepositions are very exact about location.

Yes, to a degree.

Russian lets you move parts around much more freely than English, for example:

• Чайка летит над рекой, а жук сидит у воды на камне.
• Над рекой чайка летит, а у воды на камне жук сидит.

These all describe basically the same situation.

However, the focus changes:

• putting a word earlier often makes it sound more like the topic
• putting a word later can make it sound newer or more emphasized

So the original sentence sounds very natural for describing a visual scene: first the location, then what you notice there.

No. Russian has no articles like English a and the.

So:

• чайка can mean a gull or the gull
• жук can mean a beetle or the beetle
• на камне can mean on a rock or on the rock

Context tells you which meaning is intended.

In this sentence, because it sounds like a fresh description of a scene, English will usually translate it with a:

• a gull
• a beetle
• a rock

But Russian itself does not mark that difference.

Not exactly.

• чайка usually means gull. In English, seagull is a common translation, but Russian чайка does not always specifically emphasize the sea.
• жук more specifically means beetle. In very loose translation, it may sometimes be rendered as bug, but beetle is more exact.

So if you want the most precise vocabulary sense here:

• чайка = gull
• жук = beetle

With stress marks, it is:

Над реко́й лети́т ча́йка, а у воды́ на ка́мне сиди́т жук.

A rough pronunciation guide:

• Над = naht
• реко́й = ree-KOY
• лети́т = lee-TEET
• ча́йка = CHAI-ka
• а = ah
• у = oo
• воды́ = va-DY
• на = nah
• ка́мне = KAM-nye
• сиди́т = see-DEET
• жук = zhook

A few points:

• й in чайка gives the y sound in boy
• ж in жук sounds like the s in measure
• final consonants are often pronounced more firmly than in English

If you want to sound natural, try reading it in two chunks:

• Над реко́й лети́т ча́йка,
• а у воды́ на ка́мне сиди́т жук.