This is the 1990th most frequent Swedish word.
störst
Largest.
In this sentence, 'störst' is used as a superlative adjective describing the blue whale among all creatures in the ocean.
Den blåvalen är den störst i havet.
The blue whale is the largest in the ocean.
Here, 'störst' is superlatively modifying 'industriparken', indicating the size relative to other parks in the country.
Staden har den störst industriparken i landet.
The city has the largest industrial park in the country.
'Störst' is serving as a predicate adjective describing a comparison among multiple options.