Learn Hardcore Arabic (Levantine): في ناموس جنب النهر.

Because Levantine Arabic often makes present-tense sentences without saying is or are. In this kind of sentence, في does the job of there is / there are, so a separate verb is not needed.

What does في mean here? I thought it meant in.

That is a very common question. في can mean in, but in Levantine it can also be an existential word meaning there is / there are.

So here it is not the preposition in. It is introducing the existence of something.

Why doesn’t ناموس have ال?

Because it is indefinite here. ناموس means mosquitoes in a general, non-specific sense.

ناموس = mosquitoes / some mosquitoes
الناموس = the mosquitoes

Arabic often leaves indefiniteness unmarked in dialect, so you simply see the noun without ال.

Is ناموس singular or plural?

In Levantine, ناموس is often used as a collective noun, so it can refer to mosquitoes as a group. If you want to talk about one mosquito, you would usually say ناموسة.

So:

ناموسة = one mosquito