The rise in the Irrawaddy dolphin (1) in Chilika can be attributed to the…

Concept: In a meaning-based (vocabulary) cloze blank, the correct word is the one whose dictionary sense and typical collocation match the surrounding context — not merely any grammatically valid word. For a phrase of the form ‘made ___ free’, the blank must name the specific thing that was actually removed to produce that free state.

Application: The sentence just before this blank says the rise in dolphins followed ‘the eviction of illegal fish enclosures’ — structures built inside the lake without authorisation. The blank completes ‘thousands of hectares of Chilika lake were made ___ free’, describing the direct outcome of that eviction. Removing illegal fish enclosures means removing an unauthorised occupation of the lake bed, so the cleared hectares became free of that occupation — i.e., free of ‘encroachment’, since ‘encroachment’ is precisely the word for unauthorised occupation of land or a water body.

Cross-check — why the other options do not fit:

• intervention — would mean free of any external action, but the passage explicitly describes an authority's action (eviction), so this contradicts rather than confirms the narrative.

• trespass — describes unauthorised entry by a person or animal, not the presence of a built structure standing in the water; it does not name what was cleared.

• confiscation — means officially seizing property into custody; the enclosures were evicted and removed, not taken into custody, so this sense does not match.

Result: ‘encroachment’ is the only word whose sense — unauthorised occupation of land or water — matches what was actually cleared from Chilika lake, so it correctly completes blank no. 3.