Answer: The initial answer is that you are not “required” to open the park facilities that you have kept closed. You do have some discretion on when and how to open certain non-essential park facilities.
The park does have an obligation to provide essential services like restrooms and showers if those facilities are part of what the park regularly provides to tenants. Presumably you have already been following the state guidelines for sanitation of those facilities. Under the state guidelines, facilities such as restrooms and showers should be thoroughly cleaned at least twice daily and, to the extent possible, provided with things like soap, toilet paper and hand sanitizer throughout the day.
For both essential and non-essential services, it is important to follow the state guidelines published by the Oregon Health Authority. You should go to their website for guidance on all COVID-19 issues at https://govstatus.egov.com/OR-OHA-COVID-19. The website provides general guidelines, as well as more specific guidelines for Phase 1 and Phase 2 reopening, including easy-to-print signs to post in your park regarding occupancy limits, social distancing, hand-washing, and COVID-19 symptom recognition.
With regard to reopening a swimming pool, there are very specific guidelines to follow, which include social distancing around the pool, sanitation requirements, occupancy limits, and clear signage for all of the above. The specific Phase 2 guidelines can be found here: https://sharedsystems.dhsoha.state.or.us/DHSForms/Served/le2351C.pdf.
In Phase 2, playgrounds should remain closed, and indoor rec centers should only be reopened if physical distancing can be ensured, occupancy is limited, and regular cleaning can take place, among other requirements: https://sharedsystems.dhsoha.state.or.us/DHSForms/Served/le2351A.pdf.
Ultimately, you should use your best judgment on when to reopen park facilities based on the guidelines and the park’s ability to comply with the guidelines. Your decision should also take into consideration the park’s obligation to provide park facilities to tenants under your rental agreement. While the COVID-19 emergency provides a legal justification to temporarily suspend access to those facilities, to avoid pushback from tenants you should consider reopening the facilities when it is safe and feasible under the guidelines.