sagi ha kawara ni iru.

It is read:

さぎ は かわら に いる。
Romanization: sagi wa kawara ni iru.

A few notes:

• 鷺 = さぎ = heron / egret
• は is written ha but pronounced wa when it is the topic particle
• 河原 = かわら = riverbank / riverside / dry riverbed area
• いる = to be / to exist for living things

Because here は is not part of a word; it is the topic particle.

As a particle, は is traditionally written with the kana は, but in modern Japanese it is pronounced わ.

So in this sentence:

• 鷺は = As for the heron, ... / The heron ...

This is one of the first pronunciation exceptions learners meet.

は marks the topic of the sentence.

So 鷺は means something like:

• As for the heron, ...
• The heron, ...

In natural English, we usually just say The heron is at the riverbank, but Japanese often separates the idea of topic from the idea of grammatical subject.

Here, 鷺は河原にいる presents the heron as the thing being talked about.

Here, に marks the location where something exists.

So:

• 河原にいる = is at the riverbank / is in the riverbed area

With existence verbs like いる and ある, に commonly marks the place where someone or something is.

A useful pattern is:

• place + に + いる = to be at/in a place for living things
• place + に + ある = to be at/in a place for nonliving things

Because いる is used for living, animate beings that exist somewhere.

Since a 鷺 is a bird, Japanese uses いる.

Compare:

• 鷺は河原にいる。 = The heron is at the riverbank.
• 石は河原にある。 = The stone is at the riverbank.

So the basic distinction is:

• いる → people, animals, other animate creatures
• ある → objects, things, plants in many beginner explanations, and abstract things

Because Japanese is basically an SOV language: Subject/Topic – Object/Other information – Verb.

So instead of English order:

• The heron is at the riverbank

Japanese naturally puts the verb last:

• 鷺 は 河原 に いる

This is very normal in Japanese. The main verb usually comes at the end of the sentence.

Japanese normally does not use articles like the and a/an.

So 鷺 can mean:

• a heron
• the heron
• sometimes even herons, depending on context

The exact meaning is usually understood from the situation.

In a simple isolated sentence like this, English often chooses The heron is at the riverbank or A heron is at the riverbank, but Japanese itself does not force that distinction.

Yes, 鷺が河原にいる。 is possible, but the nuance changes.

Very roughly:

• 鷺は河原にいる。 → As for the heron, it is at the riverbank.
  This sounds more like you are talking about the heron as the topic.

• 鷺が河原にいる。 → There is a heron at the riverbank / A heron is at the riverbank.
  This can sound more like introducing or identifying the heron, or emphasizing that it is the heron that is there.

For beginners, a useful shortcut is:

• は = topic / contrast / known thing
• が = subject / new information / emphasis

That is not the whole story, but it is a good start.

河原 usually means the riverbank, riverside, or the dry, stony area by a river, often like a riverbed or gravelly bank.

So it is not necessarily a grassy bank right next to the water in the English sense. It can suggest the open area along the river.

The reading is かわら.

Be careful not to confuse it with unrelated words that may sound similar.

It is a real and useful kanji, but it is not one of the very first kanji most learners master.

A few points:

• 鷺 is read さぎ
• It refers to a heron or sometimes an egret in broad everyday usage
• In many contexts, especially for learners, it may be written in kana as さぎ

So yes, it is correct, but you do not need to worry if it feels advanced as a kanji.

Because the Japanese verb いる already contains the idea of to be / to exist.

So:

• 河原にいる literally means something like exists at the riverbank for a living being

Japanese does not need a separate word equal to English is here.

This is different from sentences with です, which beginners also see a lot.
In this sentence, いる is the main verb, so です is not needed.

The polite version is:

鷺は河原にいます。

Here:

• dictionary form: いる
• polite form: います

So:

• 鷺は河原にいる。 = plain style
• 鷺は河原にいます。 = polite style

The meaning is the same, but the level of formality changes.