Yes — the sentence is correct.
Here's why, in a simple step-by-step way:
- Beavers = the subject (who the sentence is about). It is a plural noun.
- build = the verb (the action). It matches the plural subject: beavers build.
- dams and lodges = the objects (what the beavers build). There are two things, so we use "and" to join them.
- on the water = a phrase that tells where they build (a place).
All parts fit together correctly, so the grammar is fine.
Small note about word choice: "On the water" is okay, but you might also hear "in rivers and streams" because beavers usually build in rivers or streams. Both ways are correct, but they give a little different picture:
- "on the water" sounds like something sits on the water's surface.
- "in rivers and streams" tells exactly what type of water the beavers use.
Simple alternative sentence: Beavers build dams and lodges in rivers and streams.
Try this little activity: underline the subject and circle the verb in the sentence "Beavers build dams and lodges on the water."
Great job asking about grammar — you noticed a good sentence!