Wallum is in both states and falls under RI rules. Rhode Island has a "closed" season for trout. Basically Trout season is open from April 9th till Feb 28th...with a keep limit change in December through Feb. I know this because I cannot fish for carp along some of my favorite sections of the Blackstone until April 9th as well due to Rhode Island considering them trout waters.
Their site has not updated yet but the dates remain pretty much the same each year. It isn't about the opening of the park, but the opening of trout season. Below is the abstracts from the official DEM site from 2011... Page 6 and 7 or so have the open/closed info.
http://www.dem.ri.gov/programs/bnatres/fishwild/pdf/freshabs.pdf
On that note..don't plan to be there on the 9th unless you really enjoy crowds...
1. Fishing in any freshwater stream or pond within this state without
a valid fi shing license (except as noted on page 5).
2. Fishing in any stream, designated trout stream or designated trout
pond of the state, unless otherwise regulated, between 1 March
2011 and 6 AM 9 April 2011.
3. Possessing trout, salmon, or charr during the seasonal closure.
4. Using corn for bait in any trout waters.
5. Chumming in any trout waters.
6. Snagging fi sh in fresh waters.
7. Using any substance injurious to fi sh life in any stream or freshwater
pond within the state except by permit issued bythe DEM.
8. Detonating any explosive