80 Police using a water cannon against protesters, Hamburg, Germany, 6 July 2017 ©ODIHR The kinetic impact of the water can knock a person over, push them into fixed objects, or pick up loose objects and propel them as missiles. There is a risk of blunt trauma injuries when people are struck from close range. Injuries such as blindness, fractures, bruising and concussion have been reported. The United Nations Human Rights Guidance on Less-Lethal Weapons in Law Enforcement states that the targeting of a jet of water at a person or persons from close range could amount to “potentially unlawful use”.123 There are a number of ways in which the use of water cannons can pose a threat either to the physical health or human rights of participants in assemblies or bystanders, alike: Use in conditions of low (and especially sub-zero) temperatures creates the risk of hypothermia or frostbite; the mixing of malodourant into the water stream can amount to collective punishment; the use of marking dye can lead to wrongful arrests, when bystanders are marked; the use of a mixture of water and chemical irritant makes it impossible to deliver accurately targeted doses of the irritant; and the use of dirty or otherwise contaminated water can lead to negative health effects for those targeted. The ODIHR Human Rights Handbook on Policing Assemblies makes a series of recommendations on the use of water cannons.124 The most pertinent for monitors are that: 123 UN, Guidance on Less-Lethal Weapons in Law Enforcement, op. cit., note 7, para. 7.7.4. 124 ODIHR, Human Rights Handbook on Policing Assemblies, op. cit., note 2, pp. 77-78.