Basement drain without a trap
In the short term, try 5-10% bleach solution in water, not just water. i.e. a cup of bleach to a gallon of water (1:15, or about 6.7%)

It may be a "floor drain to soakaway" rather than connected to septic/sewer, but those can still get quite nasty (especially if something crawls down there and dies).

A "test plug" can give you a way to reversibly plug it until you decide what to do about it in the long term. Image for illustration only, does not imply endorsement of any particular brand or store:



Responding to Comment:



To determine if the drain is or is not connected to septic/sewer: Access manhole at septic tank or sewer connection. Pour non-toxic septic dye into drain. See if it shows up at the septic/sewer. On a public sewer you will need the cooperation of the sewer department as they take an understandably dim view of the public opening their manholes for safety reasons, unless you have a sewer cleanout before the street that you can look into and spot the dye (or lack.) If you don't see the dye, the pipe presumably does not connect to the septic/sewer.

As for why it might not connect to the sewer/septic - to reduce volume handled by septic/sewer, or because the sewer pipe is higher than the floor and the drain was installed before drain pumps were popular/common. Floor drain waste should not be particularly pathogenic or contain septic waste, and particularly in older systems design to limit "non-septic" waste going into the septic was quite common, to limit the load on systems that were quite small by current standards. In a fully configured city environment it might connect to a storm drain rather than a sanitary sewer for similar reasons.