Possible Clues:

• Summer social event
• Summertime backyard bash, and a hint to the ends of 17-, 25-, 40-, and 50-Across
• Splashy bash
• Gathering where one might make a splash
• 'Splashy' summer bash
• Place to make a splash
• Bash with a splash
• Summer shindig, and a hint to the starts of 17-, 24-, 41- and 51-Across