[SoftTalker]

In the absence of the canal, did these lakes naturally drain to the sea, or are they in some sort of natural "bowl" that is higher than sea level?

[kzrdude]

See the cross section

https://kids.britannica.com/students/assembly/view/68621

"Natural bowl higher than sea level" could be called a lake.

[marcosdumay]

Very few lakes on the planted don't drain to the sea. They are usually salty, smelly water bodies that nobody wants to be around.