kawara wo aruku.

It is usually read かわら.

So the full sentence is:

かわら を あるく。

A useful note: 河原 is also very commonly written 川原, and that is also read かわら.

河原 means the riverbank, riverside, or sometimes the dry riverbed / stony area by a river.

It does not just mean the water itself. It refers to the area along the river, often the open ground beside it.

So in this sentence, the person is walking along / on the riverbank.

This is a very common learner question.

Yes, を often marks the direct object, but that is not its only use. With movement verbs like 歩く (to walk), を can mark the place that someone moves through, along, or across.

So in:

河原を歩く

the riverbank is not a direct object in the English sense. It is the route / area traversed.

You can think of it like:

• walk along the riverbank
• walk on the riverbank
• walk through the riverbank area

This use also appears in sentences like:

• 道を歩く = walk along the road
• 橋を渡る = cross the bridge
• 公園を走る = run through the park

This is about the difference between を and で.

• 河原を歩く focuses on the path/area being traversed
• 河原で歩く would focus more on the location where the action happens

With 歩く, を is very natural when you imagine moving along a route or through an area.

So:

• 河原を歩く = walk along/on the riverbank

  • natural and common
  • emphasizes movement through that space

• 河原で歩く = walk at the riverbank

  • grammatically possible in some contexts
  • focuses more on the place where the walking happens, not the path
  • often sounds less natural if you simply mean walking along the riverbank

In many cases, を is the better choice with 歩く when the place is being traversed.

歩く is the plain non-past form.

In Japanese, the non-past can mean:

• present / habitual: someone walks there regularly
• future: someone will walk there
• sometimes a general statement: walking on the riverbank

So without context, 河原を歩く could mean:

• walk along the riverbank
• walks along the riverbank
• will walk along the riverbank

Japanese often leaves that kind of detail to context.

Because Japanese often omits the subject when it is already understood from context.

So 河原を歩く。 could mean:

• I walk along the riverbank
• He walks along the riverbank
• She will walk along the riverbank
• They walk along the riverbank

The sentence is still completely natural without a stated subject.

This is one of the biggest differences from English: Japanese does not need to say the subject if it is obvious or unimportant.

歩く is basically an intransitive verb: it means to walk, not to walk something.

That is why the を here can confuse learners. But again, in this pattern, を is not marking a normal direct object. It is marking the route or space moved through.

So even though 歩く is intransitive, 河原を歩く is perfectly normal Japanese.

Yes, depending on the context and translation style.

A very literal interpretation is:

• walk along the riverbank
• walk on the riverbank

A more natural English translation in some contexts might be:

• walk by the river
• take a walk along the riverside

So the exact English wording can vary, even though the Japanese is the same.

Yes. That would mean is walking along the riverbank.

Compare:

• 河原を歩く
  plain non-past
  = walk / walks / will walk along the riverbank

• 河原を歩いている
  progressive / ongoing action
  = is walking along the riverbank

If you want to describe someone in the middle of the action right now, 歩いている is usually the better form.

Yes, absolutely.

Japanese often allows very short sentences when the context fills in the missing information. Here, the sentence has:

• a noun: 河原
• a particle: を
• a verb: 歩く

That is enough to form a natural sentence.

It may feel incomplete to an English speaker because English usually wants an explicit subject, but in Japanese this is normal.