Hydro Hills is rather easy for players accustomed to previous park value objective scenarios (such as Dinky Park, Diamond Heights, and Katie's World, for example). Research should be set to roller coasters, thrill & gentle rides, and shops/stalls to maximum funding. Two Shuttle Loops next to each other and set to launch simultaneously, would be a solid start. This will boost excitement, as well as give them identical loading rates. Some gentle and thrill rides scattered around the bottom lake, will bring in some guests and will also make some solid money to start with.
A nice trick with this park is to build in each lake as the park expands. This prevents overcrowding, as in RCT1 wide paths do hardly work in this matter. Two-tile paths barely work in RCT2, and the problem's actually addressed in OpenRCT2. In the original game, cramming all rides in the first lake without a properly planned layout, will bring the overcrowding issue in no time.
By the end, players should have around 4-7 coasters (excluding the Shuttle Loops) and lots of flat rides scattered around the park, as well as the loan paid off and a park value close to $30,000, much more than what the objective requires. Deleting the pre-built boat hire shouldn't be necessary at all, though closing the track into a partial or full circuit and/or landscaping around it to prevent boats from getting stuck can help it be more successful.