Explanation:

- Rotterdam (Option 1):

The Port of Rotterdam is actually a riverine port, located on the banks of the Nieuwe Maas channel in the Rhine-Meuse delta, not specifically an estuarine port.

- Port of Singapore (Option 2):

Singapore is a major seaport and is located on the southern end of the Malay Peninsula, but it is not classified as an estuarine port; rather, it’s a natural deep-water port.

- Marmagao Port (Option 3):

Marmagao (or Mormugao) port, situated in Goa, India, is an estuarine port, as it is located at the mouth of the Zuari River where the river meets the Arabian Sea.

- Port of Toronto (Option 4):

The Port of Toronto is on the Lake Ontario shoreline, and is not an estuarine port.

The correct answer is Option 3: Marmagao port