Learn Croatian: Ovo jezero je plavo.

In Croatian, adjectives must match the gender of the noun they describe. Because jezero (lake) is a neuter noun, the adjective takes the neuter ending -o, making it plavo. If the noun were masculine, it would be plav, and if feminine, plava.

Why do we use Ovo for 'This'?

Just like adjectives, pointing words like 'this' have to match the noun's gender. Ovo is the neuter form of 'this' to match the neuter noun jezero. For a masculine noun, you would use ovaj, and for a feminine noun, ova.

How can I tell that jezero is a neuter noun?

You can usually guess a noun's gender by its last letter in its basic dictionary form. Nouns that end in -o or -e are almost always neuter.

I learned that je (is) has to be the second word in a sentence. Why is it the third word here?

je is a special type of short, unstressed word that needs to be in the second position of a sentence. However, Ovo jezero (This lake) acts together as a single phrase. Therefore, the entire phrase counts as the first block of information, placing je safely in the second position!