There is no river at 30 degrees north and 40 degrees east.
The Karun River
30 degrees north and 150 degrees east is in the North Pacific, southeast of Tokyo, near where Godzilla was created.
30 degrees north and 55 degrees east is in Iran.
The Himalayas are at 30 degrees north and 82 degrees east.
Asia is at 30 degrees north and 105 degrees east.
30 degrees north and 138 degrees east is in the Pacific Ocean. The point is south of Japan and east of China.
30 degrees north and 21 degrees east is in Libya, on the continent of Africa. It is southwest of Aidabiya.
It is the Persian Gulf, which is actually an arm of an ocean or sea rather than a river.
30 degrees north and 48 degrees east is the mouth of the Euphrates River, in Iraq, on the continent of Asia.
Karun River
30 degrees north and 125 degrees east intersect in the South China Sea, off the coast of China. Shanghai is nearby, at about 31 degrees north and 121 degrees east.
30 degrees north and 59 degrees east is in southeastern Iran, about 115 miles east-southeast of Kerman. It is on the continent of Asia.