Hi Mac
It looks like a lovely place, but it doesn't sound like you had the best experience. They should really hire someone to clean up the trash at least especially if they want to open it up as a tourist destination spot. The mosquitoes would have been a big turn off for me too.
They already have one for "tourist" spot. Meanwhile that place is the free and open space and often visited by locals or just anyone who likes fishing. Although to be fair, since it also belongs to similar management, they should do that too. It's only wishful thinking to hope these beautiful places all around would be free of litters. The only clean ones are those for "tourist" and intended to be visited by foreigners too.
That's the sad reality. It happens here as well that the open parks look terrible after busy weekends and the litter ends up in the river systems. It annoys me no end, but people just don't care enough to manage their own waste and the management don't care enough to enforce it. The cleanest places in the world are the ones with the heftiest fines for littering. If you can't teach them by asking nicely, you have to make them do it by hitting them where it hurts, that is just the sad reality of it.