I am looking for help choosing spells for an upcoming underwater adventure. I am a level 7 Druid with a 20 Wisdom and a Scorpion companion who will be eating one spell for Ride the Waves(UM). My build is focused on summoning but I want summoning doesn't always happen. Though I wouldn't be adverse to summon selection advice. I will be accompanied by a witch and a hex magus to help with lowering saving throws.
Hydrophobia is going to be a reliably disabling spell underwater. If you want a direct attack spell look at explosion of rot and/or burst of radiance.
Since most aquatic creatures are going to be faster than 30' base speed you may want tail current to speed your party up. Poison is pretty common in aquatic creatures too, make sure you have delay poison or invigorating poison.
Buffs will generally be just as good below water as they are above.