11.09.2020. Latvian government published information: https://www.spkc.gov.lv/sites/spkc/files/data_content/11_09_2020
Athletes from Finland and Lithuania can participate in our race without staying in quarantine, Estonia at the moment should abide quarantine. BUT according Latvian law, athletes can participate in sport event from other countries like Estonia without staying in quarantine, if they follow the rules:

61.4 Athletes and sports employees, and also representatives of international sports organisations whose arrival in the territory of the Republic of Latvia is connected with participation as an accredited person in an international sporting event organised by a sports federation recognised in accordance with the procedures laid down by the Sports Law or a member thereof, and who have arrived from a country which is published on the website of the Centre as a country to which the special precautionary and restrictive measures are applicable shall not be subject to the requirement referred to in Sub-paragraph 56.1 of this Regulation for self-isolation and the requirement referred to in Sub-paragraph 56.2 of this Regulation for the visiting of social and public spaces and premise and contacts with other persons at a place and time when the person fulfils such duties which are directly related to participation in the international sporting event if the person meets the following criteria:
61.4 1. the person does not display signs of an acute respiratory disease;
61.4 2. the person can submit to the organiser of the international sporting event in Latvia a copy of the document (present the original thereof upon a request) certifying that he or she has undergone laboratory testing for the diagnostics of COVID-19 not earlier than three days before arrival in the territory of the Republic of Latvia and it did not find COVID-19 infection;
61.4 3. not later than 24 hours after arrival in the territory of the Republic of Latvia, the person has undergone laboratory testing for the diagnostics of COVID-19 and it did not find COVID-19 infection, and the person has also submitted a copy of the document certifying this fact (presented the original thereof upon a request) to the responsible medical practitioner appointed by the organiser of the international sporting event in Latvia;
61.4 4. before arrival in the territory of the Republic of Latvia (concurrently with accreditation for the international sporting event) or not later than 24 hours after arrival in the territory of the Republic of Latvia, the person has submitted to the organiser of the international sporting event in Latvia a certification that:
61.4 4.1. he or she shall comply with all the restrictions imposed for the prevention of the spread of COVID-19 infection, including the conditions referred to in Sub-paragraphs 56.2, 61.4 4.2, 61.4 4.3 and 61.4 4.4, and also Paragraph 61.2 of this Regulation (where applicable);
61.4 4.2. outside the participation in the international sporting event he or she shall stay at the place of stay in the Republic of Latvia indicated in the certification;
61.4 4.3. during the stay in the territory of the Republic of Latvia, he or she shall monitor his or her health condition (two times per day - in the morning and evening - by measuring body temperature) and shall inform the responsible medical practitioner appointed by the organiser of the international sporting event in Latvia if any signs of an acute respiratory disease (cough, increased body temperature (fever), shortness of breath) appear;
61.4 4.4. he or she shall not use the public transportation, and also shall use personal vehicle or a vehicle ensured by the organiser of the international sporting event in Latvia to get to the place of stay in the territory of the Republic of Latvia and venue of the international sporting event in the territory of the Republic of Latvia, and when travelling between these places;
61.4 4.5. he or she shall cover all the expenditures related to medical treatment if COVID-19 infection will be confirmed to the person.

LAW: https://likumi.lv/ta/en/en/id/315304-epidemiological-safety-measures-for-the-containment-of-the-spread-of-covid-19-infection